Section II. THEORY
1-3. GENERAL Welding is any metal joining process wherein coalescence is produced by heating the metal to suitable temperatures, with or without the application of pressure and with or without the use of filler metals. Basic welding processes are described and illustrated in this manual. Brazing and soldering, procedures similar to welding, are also covered. 1-4. METALS a. Metals are divided into two classes, ferrous and nonferrous. Ferrous metals are those in the iron class and are magnetic in nature. These metals consist of iron, steel, and alloys related to them. Nonferrous metals are those that contain either no ferrous metals or very small amounts. These are generally divided into the aluminum, copper, magnesium, lead, and similar groups. b. Information contained in this circular covers theory and application of welding for all types of metals including recently developed alloys.

CHAPTER 2 SAFETY PRECAUTIONS IN WELDING OPERATIONS

Section I. GENERAL SAFETY PRECAUTIONS
2-1. GENERAL a. To prevent injury to personnel, extreme caution should be exercised when using any types of welding equipment. Injury can result from fire, explosions, electric shock, or harmful agents. Both the general and specific safety precautions listed below must be strictly observed by workers who weld or cut metals. b. Do not permit unauthorized persons to use welding or cutting equipment. c. Do not weld in a building with wooden floors, unless the floors are protected from hot metal by means of fire resistant fabric, sand, or other fireproof material. Be sure that hot sparks or hot metal will not fall on the operator or on any welding equipment components. d. Remove all flammable material, such as cotton, oil, gasoline, etc., from the vicinity of welding. e. Before welding or cutting, warm those in close proximity who are not protected to wear proper clothing or goggles. f. Remove any assembled parts from the component being welded that may become warped or otherwise damaged by the welding process. g. Do not leave hot rejected electrode stubs, steel scrap, or tools on the floor or around the welding equipment. Accidents and/or fires may occur. h. Keep a suitable fire extinguisher nearby at all times. Ensure the fire extinguisher is in operable condition. i. Mark all hot metal after welding operations are completed. Soapstone is commonly used for this purpose. 2-2. PERSONAL PROTECTIVE EQUIPMENT a. General. The electric arc is a very powerful source of light, including visible, ultraviolet, and infrared. Protective clothing and equipment must be worn during all welding operations. During all oxyacetylene welding and cutting proccesses, operators must use safety goggles to protect the eyes from heat, glare, and flying fragments of hot metals. During all electric welding processes, operators must use safety goggles and a hand shield or helmet equipped with a suitable filter

glass to protect against the intense ultraviolet and infrared rays. When others are in the vicinity of the electric welding processes, the area must be screened so the arc cannot be seen either directly or by reflection from glass or metal. b. Helmets and Shields. (1) Welding arcs are intensely brilliant lights. They contain a proportion of ultraviolet light which may cause eye damage. For this reason, the arc should never be viewed with the naked eye within a distance of 50.0 ft (15.2 m). The brilliance and exact spectrum, and therefore the danger of the light, depends on the welding process, the metals in the arc, the arc atmosphere, the length of the arc, and the welding current. Operators, fitters, and those working nearby need protection against arc radiation. The intensity of the light from the arc increases with increasing current and arc voltage. Arc radiation, like all light radiation, decreases with the square of the distance. Those processes that produce smoke surrounding the arc have a less bright arc since the smoke acts as a filter. The spectrum of the welding arc is similar to that of the sun. Exposure of the skin and eyes to the arc is the same as exposure to the sun. (2) Being closest, the welder needs a helmet to protect his eyes and face from harmful light and particles of hot metal. The welding helmet (fig. 2-1) is generally constructed of a pressed fiber insulating material. It has an adjustable headband that makes it usable by persons with different head sizes. To minimize reflection and glare produced by the intense light, the helmet is dull black in color. It fits over the head and can be swung upward when not welding. The chief advantage of the helmet is that it leaves both hands free, making it possible to hold the work and weld at the same time.

(3) The hand-held shield (fig. 2-1) provides the same protection as the helmet, but is held in position by the handle. This type of shield is frequently used by an observer or a person who welds for a short period of time. (4) The protective welding helmet has lens holders used to insert the cover glass and the filter glass or plate. Standard size for the filter plate is 2 x 4-1/4 in. (50 x 108 mm). In some helmets lens holders open or flip upwards. Lenses are designed to prevent flash

burns and eye damage by absorption of the infrared and ultraviolet rays produced by the arc. The filter glasses or plates come in various optical densities to filter out various light intensities, depending on the welding process, type of base metal, and the welding current. The color of the lens, usually green, blue, or brown, is an added protection against the intensity of white light or glare. Colored lenses make it possible to clearly see the metal and weld. Table 2-1 lists the proper filter shades to be used. A magnifier lens placed behind the filter glass is sometimes used to provide clear vision.

A cover plate should be placed outside the filter glass to protect it from weld spatter. The filter glass must be tempered so that is will not break if hit by flying weld spatter. Filter glasses must be marked showing the manufacturer, the shade number, and the letter “H” indicating it has been treated for impact resistance. NOTE

Colored glass must be manufactured in accordance with specifications detailed in the “National Safety Code for the Protection of Hands and Eyes of Industrial Workers”, issued by the National Bureau of Standards, Washington DC, and OSHA Standards, Subpart Q, “Welding, Cutting, and Brazing”, paragraph 1910.252, and American National Standards Institute Standard (ANSI) Z87.1-1968, “American National Standard Practice for Occupational and Educational Eye and Face Protection”. (5) Gas metal-arc (MIG) welding requires darker filter lenses than shielded metal-arc (stick) welding. The intensity of the ultraviolet radiation emitted during gas metal-arc welding ranges from 5 to 30 times brighter than welding with covered electrodes. (6) Do not weld with cracked or defective shields because penetrating rays from the arc may cause serious burns. Be sure that the colored glass plates are the proper shade for arc welding. Protect the colored glass plate from molten metal spatter by using a cover glass. Replace the cover glass when damaged or spotted by molten metal spatter. (7) Face shields (fig. 2-2) must also be worn where required to protect eyes. Welders must wear safety glasses and chippers and grinders often use face shields in addition to safety glasses.

(8) In some welding operations, the use of mask-type respirators is required. Helmets with the "bubble" front design can be adapted for use with respirators. c. Safety Goggles. During all electric welding processes, operators must wear safety goggles (fig. 2-3) to protect their eyes from weld spatter which occasionally gets inside the helmet. These clear goggles also protect the eyes from slag particles when chipping and hot sparks when grinding. Contact lenses should not be worn when welding or working around welders. Tinted safety glasses with side shields are recommended, especially when welders are chipping or grinding. Those working around welders should also wear tinted safety glasses with side shields.

d. Protective Clothing. (1) Personnel exposed to the hazards created by welding, cutting, or brazing operations shall be protected by personal protective equipment in accordance with OSHA standards, Subpart I, Personal Protective Equipment, paragraph 1910.132. The appropriate protective clothing (fig. 2-4) required for any welding operation will vary with the size, nature, and location of the work to be performed. Welders should wear work or shop clothes without openings or gaps to prevent arc rays from contacting the skin. Those working close to arc welding should also wear protective clothing. Clothing should always be kept dry, including gloves.

(2) Woolen clothing should be worn instead of cotton since wool is not easily burned or damaged by weld spatter and helps to protect the welder from changes in temperature. Cotton clothing, if used, should be chemically treated to reduce its combustibility. All other clothing, such as jumpers or overalls, should be reasonably free from oil or grease. (3) Flameproof aprons or jackets made of leather, fire resistant material, or other suitable material should be worn for protection against spatter of molten metal, radiated heat, and

sparks. Capes or shoulder covers made of leather or other suitable materials should be worn during overhead welding or cutting operations. Leather skull caps may be worn under helmets to prevent head burns. (4) Sparks may lodge in rolled-up sleeves, pockets of clothing, or cuffs of overalls and trousers. Therefore, sleeves and collars should be kept buttoned and pockets should be eliminated from the front of overalls and aprons. Trousers and overalls should not be turned up on the outside. For heavy work, fire-resisant leggings, high boots, or other equivalent means should be used. In production work, a sheet metal screen in front of the worker’s legs can provide further protection against sparks and molten metal in cutting operations. (5) Flameproof gauntlet gloves, preferably of leather, should be worn to protect the hands and arms from rays of the arc, molten metal spatter, sparks, and hot metal. Leather gloves should be of sufficient thickness so that they will not shrivel from the heat, burn through, or wear out quickly. Leather gloves should not be used to pick up hot items, since this causes the leather to become stiff and crack. Do not allow oil or grease to cane in contact with the gloves as this will reduce their flame resistance and cause them to be readily ignited or charred. e. Protective Equipment. (1) Where there is exposure to sharp or heavy falling objects or a hazard of bumping in confined spaces, hard hats or head protectors must be used. (2) For welding and cutting overhead or in confined spaces, steel-toed boots and ear protection must also be used. (3) When welding in any area, the operation should be adequately screened to protect nearby workers or passers-by froman the glare of welding. The screens should be arranged so that no serious restriction of ventilation exists. The screens should be mounted so that they are about 2.0 ft above the floor unless the work is performed at such a low level that the screen must be extended closer to the floor to protect adjacent workers. The height of the screen is normally 6.0 ft (1.8 m) but may be higher depending upon the situation. Screen and surrounding areas must be painted with special paints which absorb ultraviolet radiation yet do not create high contrast between the bright and dark areas. Light pastel colors of a zinc or titanium dioxide base paint are recommended. Black paint should not be used. 2-3. FIRE HAZARDS a. Fire prevention and protection is the responsibility of welders, cutters, and supervisors. Approximately six percent of the fires in industrial plants are caused by cutting and welding which has been done primarily with portable equipment or in areas not specifically designated for such work. The elaboration of basic precautions to be taken for fire prevention during welding or cutting is found in the Standard for Fire Prevention in Use of Cutting and Welding

Processes, National Fire Protection Association Standard 51B, 1962. Some of the basic precautions for fire prevention in welding or cutting work are given below. b. During the welding and cutting operations, sparks and molten spatter are formal which sometimes fly considerable distances. Sparks have also fallen through cracks, pipe holes, or other small openings in floors and partitions, starting fires in other areas which temporarily may go unnoticed. For these reasons, welding or cutting should not be done near flammable materials unless every precaution is taken to prevent ignition. c. Hot pieces of base metal may come in contact with combustible materials and start fires. Fires and explosions have also been caused when heat is transmitted through walls of containers to flammable atmospheres or to combustibles within containers. Anything that is combustible or flammable is susceptible to ignition by cutting and welding. d. When welding or cutting parts of vehicles, the oil pan, gasoline tank, and other parts of the vehicle are considered fire hazards and must be removed or effectively shielded from sparks, slag, and molten metal. e. Whenever possible, flammable materials attached to or near equipment requiring welding, brazing, or cutting will be removed. If removal is not practical, a suitable shield of heat resistant material should be used to protect the flammable material. Fire extinguishing equipment, for any type of fire that may be encountered, must be present. 2-4. HEALTH PROTECTION AND VENTILATION a. General. (1) All welding and thermal cutting operations carried on in confined spaces must be adequately ventilated to prevent the accumulation of toxic materials, combustible gases, or possible oxygen deficiency. Monitoring instruments should be used to detect harmful atmospheres. Where it is impossible to provide adequate ventilation, air-supplied respirators or hose masks approved for this purpose must be used. In these situations, lookouts must be used on the outside of the confined space to ensure the safety of those working within. Requirements in this section have been established for arc and gas welding and cutting. These requirements will govern the amount of contamination to which welders may be exposed: (a) Dimensions of the area in which the welding process takes place (with special regard to height of ceiling). (b) Number of welders in the room. (c) Possible development of hazardous fumes, gases, or dust according to the metals involved. (d) Location of welder's breathing zone with respect to rising plume of fumes.

(2) In specific cases, there are other factors involved in which respirator protective devices (ventilation) should be provided to meet the equivalent requirements of this section. They include: (a) Atomspheric conditions. (b) Generated heat. (c) Presence of volatile solvents. (3) In all cases, the required health protection, ventilation standards, and standard operating procedures for new as well as old welding operations should be coordinated and cleaned through the safety inspector and the industrial hygienist having responsibility for the safety and health aspects of the work area. b. Screened Areas. When welding must be performed in a space entirely screened on all sides, the screens shall be arranged so that no serious restriction of ventilation exists. It is desirable to have the screens mounted so that they are about 2.0 ft (0.6 m) above the floor, unless the work is performed at such a low level that the screen must be extended closer to the floor to protect workers from the glare of welding. See paragraph 2-2 e (3). c. Concentration of Toxic Substances. Local exhaust or general ventilating systems shall be provided and arranged to keep the amount of toxic frees, gas, or dusts below the acceptable concentrations as set by the American National Standard Institute Standard 7.37; the latest Threshold Limit Values (TLV) of the American Conference of Governmental Industrial Hygienists; or the exposure limits as established by Public Law 91-596, Occupational Safety and Health Act of 1970. Compliance shall be determined by sampling of the atmsphere. Samples collected shall reflect the exposure of the persons involved. When a helmet is worn, the samples shall be collected under the helmet. NOTE Where welding operations are incidental to general operations, it is considered good practice to apply local exhaust ventilation to prevent contamination of the general work area. d. Respiratory Protective Equipment. Individual respiratory protective equipment will be well retained. Only respiratory protective equipment approved by the US Bureau of Mines, National Institute of Occupational Safety and Health, or other government-approved testing agency shall be utilized. Guidance for selection, care, and maintenance of respiratory protective equipment is given in Practices for Respiratory Protection, American National Standard Institute Standard 788.2 and TB MED 223. Respiratory protective equipment will not be transferred from one individual to another without being disinfected. e. Precautionary Labels. A number of potentially hazardous materials are used in flux coatings, coverings, and filler metals. These materials, when used in welding and cutting operations, will become hazardous to the welder as they are released into the atmosphere. These include, but are not limited to, the following materials: fluorine compounds, zinc, lead, beryllium, cadmium, and

mercury. See paragraph 2-4 i through 2-4 n. The suppliers of welding materials shall determine the hazard, if any, associated with the use of their materials in welding, cutting, etc. (1) All filler metals and fusible granular materials shall carry the following notice, as a minimum, on tags, boxes, or other containers: CAUTION Welding may produce fumes and gases hazardous to health. Avoid breathing these fumes and gases. Use adequate ventilation. See American National Standards Institute Standard Z49.11973, Safety in Welding and Cutting published by the American Welding Society. (2) Brazing (welding) filler metals containing cadmium in significant amounts shall carry the following notice on tags, boxes, or other containers: WARNING CONTAINS CADMIUM - POISONOUS FUMES MAY BE FORMED ON HEATING Do not breathe fumes. Use only with adequate ventilation, such as fume collectors, exhaust ventilators, or air-supplied respirators. See American National Standards Institute Standard Z49.1-1973. If chest pain, cough, or fever develops after use, call physician immediately. (3) Brazing and gas welding fluxes containing fluorine compounds shall have a cautionary wording. One such wording recommended by the American Welding Society for brazing and gas welding fluxes reads as follows: CAUTION CONTAINS FLUORIDES This flux, when heated, gives off fumes that may irritate eyes, nose, and throat. Avoid fumes--use only in well-ventilated spaces. Avoid contact of flux with eyes or skin. Do not take internally. f. Ventilation for General Welding and Cutting. (1) General. Mechanical ventilation shall be provided when welding or cutting is done on metals not covered in subparagraphs i through p of this section, and under the following conditions: (a) In a space of less than 10,000 cu ft (284 cu m) per welder. (b) In a roan having a ceiling height of less than 16 ft (5 m). (c) In confined spaces or where the welding space contains partitions, balconies, or other structural barriers to the extent that they significantly obstruct cross ventilation.

(2) Minimum rate. Ventilation shall be at the minimum rate of 200 cu ft per minute (57 cu m) per welder, except where local exhaust heeds, as in paragraph 2-4 g below, or airline respirators approved by the US Bureau of Mines, National Institute of Occupational Safety and Health, or other government-approved testing agency, are used. When welding with rods larger than 3/16 in. (0.48 cm) in diameter, the ventilation shall be higher as shown in the following: Rod diameter (inches) 1/4 (0.64 cm) 3/8 (0.95 cm) Required ventilation (cfm) 3500 4500

Natural ventilation is considered sufficient for welding or cutting operations where the conditions listed above are not present. Figure 2-5 is an illustration of a welding booth equipped with mechanical ventilation sufficient for one welder.

g. Local Exhaust Ventilation. Mechanical local exhaust ventilation may be obtained by either of the following means:

(1) Hoods. Freely movable hoods or ducts are intended to be placed by the welder as near as practicable to the work being welded. These will provide a rate of airflow sufficient to maintain a velocity the direction of the hood of 100 in linear feet per minute in the zone of welding. The ventilation rates required to accomplish this control velocity using a 3-in. wide flanged suction opening are listed in table 2-2.

(2) Fixed enclosure. A fixed enclosure with a top and two or more sides which surrounds the welding or cutting operations will have a rate of airflow sufficient to maintain a velocity away from the welder of not less than 100 linear ft per minute. Downdraft ventilation tables require 150 cu ft per minute per square foot of surface area. This rate of exhausted air shall be uniform across the face of the grille. A low volume, high-density fume exhaust device attached to the welding gun collects the fumes as close as possible to the point of origin or at the arc. This method of fume exhaust has become quite popular for the semiautomatic processes, particularly the flux-cored arc welding process. Smoke exhaust systems incorporated in semiautomatic guns provide the most economical exhaust system since they exhaust much less air they eliminate the need for massive air makeup units to provide heated or cooled air to replace the air exhausted. Local ventilation should have a rate of air flow sufficient to maintain a velocity away from the welder of not less than 100 ft (30 m) per minute. Air velocity is measurable using a velometer or air flow inter. These two systems can be extremely difficult to use when welding other than small weldments. The down draft welding work tables are popular in Europe but are used to a limited degree North America. In all cases when local ventilation is used, the exhaust air should be filtered. h. Ventilation in Confined Spaces. (1) Air replacement. Ventilation is a perquisite to work in confined spaces. All welding and cutting operations in confined spaces shall be adequately ventilated to prevent the accumulation of toxic materials -or possible oxygen deficiency. This applies not only to the welder but also to helpers and other personnel in the immediate vicinity. (2) Airline respirators. In circumstances where it is impossible to provide adequate ventilation in a confined area, airline respirators or hose masks, approved by the US Bureau of Mines, National Institute of Occupational Safety and Health, or other government-approved testing agency, will be used for this purpose. The air should meet the standards established by Public Law 91-596, Occupational Safety and Health Act of 1970.

(3) Self-contained units. In areas immediately hazardous to life, hose masks with blowers or self-contained breathing equipment shall be used. The breathing equipment shall be approved by the US Bureau of Mines or National Institute of Occupational Safety and Health, or other government-approved testing agency. (4) Outside helper. Where welding operations are carried on in confined spaces and where welders and helpers are provided with hose masks, hose masks with blowers, or self-contained breathing equipment, a worker shall be stationed on the outside of such confined spaces to ensure the safety of those working within. (5) Oxygen for ventilation. Oxygen must never be used for ventilation. i. Fluorine Compounds. (1) General. In confined spaces, welding or cutting involving fluxes, coverings, or other materials which fluorine compounds shall be done in accordance with paragraph 2-4 h, ventilation in confined spaces. A fluorine compound is one that contains fluorine as an element in chemical combination, not as a free gas. (2) Maximum allowable concentration. The need for local exhaust ventilation or airline respirators for welding or cutting in other than confined spaces will depend upon the individual circumstances. However, experience has shown that such protection is desirable for fixed-location production welding and for all production welding on stainless steels. When air samples taken at the welding location indicate that the fluorides liberated are below the maximum allowable concentration, such protection is not necessary. j. Zinc. (1) Confined spaces. In confined spaces, welding or cutting involving zinc-bearing filler metals or metals coated with zinc-bearing materials shall be done in accordance with paragraph 2-4 h, ventilation in confined spaces. (2) Indoors. Indoors, welding or cutting involving zinc-bearing metals or filler metals coated with zinc-bearing materials shall be done in accordance with paragraph 2-4 g. k. Lead. (1) Confined spaces. In confined spaces, welding involving lead-base metals (erroneously called lead-burning) shall be done in accordance with paragraph 2-4 h. (2) Indoors. Indoors, welding involving lead-base metals shall be done in accordance with paragraph 2-4 g, local exhaust ventilation. (3) Local ventilation. In confined spaces or indoors, welding or cutting involving metals containing lead or metals coated with lead-bearing materials, including paint, shall be

done using local exhaust ventilation or airline respirators. Outdoors, such operations shall be done using respirator protective equipment approved by the US Bureau of Mines, National Institute of Occupational Safety and Health, or other government-approved testing agency. In all cases, workers in the immediate vicinity of the cutting or welding operation shall be protected as necessary by local exhaust ventilation or airline respirators. l. Beryllium. Welding or cutting indoors, outdoors, or in confined spaces involving berylliumbearing material or filler metals will be done using local exhaust ventilation and airline respirators. This must be performed without excep-tion unless atmospheric tests under the most adverse conditions have established that the workers’ exposure is within the acceptable concentrations of the latest Threshold Limit Values (TLV) of the American Conference of Governmental Industrial Hygienists, or the exposure limits established by Public Law 91-596, Occupational Safety and Health Act of 1970. In all cases, workers in the immediate vicinity of the welding or cutting operations shall be protected as necessary by local exhaust ventilation or airline respirators. m. Cadmium. (1) General. Welding or cutting indoors or in confined spaces involving cadmium-bearing or cadmium-coated base metals will be done using local exhaust ventilation or airline respirators. Outdoors, such operations shall be done using respiratory protective equipment such as fume respirators, approved by the US Bureau of Mines, National Institute of Occupational Safety and Health, or other government-approved testing agency, for such purposes. (2) Confined space. Welding (brazing) involving cadmium-bearing filler metals shall be done using ventilation as prescribed in paragraphs 2-4 g, local exhaust ventilation, and 24 h, ventilation in confined spaces, if the work is to be done in a confined space. NOTE Cadmium-free rods are available and can be used in most instances with satisfactory results. n. Mercury. Welding or cutting indoors or in a confined space involving metals coated with mercury-bearing materials, including paint, shall be done using local exhaust ventilation or airline respirators. Outdoors, such operations will be done using respiratory protective equipment approved by the National Institute of Occupational Safety and Health, US Bureau of Mines, or other government-approved testing agency. o. Cleaning Compounds. (1) Manufacturer’s instructions. In the use of cleaning materials, because of their toxicity of flammability, appropriate precautions listed in the manufacturer’s instructions will be followed.

(2) Degreasing. Degreasing or other cleaning operations involving chlorinated hydrocarbons will be located so that no vapors from these operations will reach or be drawn into the area surrounding any welding operation. In addition, trichloroethylene and perchloroethylene should be kept out of atmospheres penetrated by the ultraviolet radiation of gas-shielded welding operations. p. Cutting of Stainless Steels. Oxygen cutting, using either a chemical flux or iron powder, or gas-shielded arc cutting of stainless steel will be done using mechanical ventilation adequate to remove the fumes generated. q. First-Aid Equipment. First-aid equipment will be available at all times. On every shift of welding operations, there will be personnel present who are trained to render first-aid. All injuries will be reported as soon as possible for medical attention. First-aid will be rendered until medical attention can be provided. 2-5. WELDING IN CONFINED SPACES a. A confined space is intended to mean a relatively small or restricted space such as a tank, boiler, pressure vessel, or small compartment of a ship or tank. b. When welding or cutting is being performed in any confined space, the gas cylinders and welding machines shall be left on the outside. Before operations are started, heavy portable equipment mounted on wheels shall be securely blocked to prevent accidental movement. c. Where a welder must enter a confined space through a manhole or other all opening, means will be provided for quickly removing him in case of emergency. When safety belts and life lines are used for this purpose, they will be attached to the welder’s body so that he cannot be jammed in a small exit opening. An attendant with a preplanned rescue procedure will be stationed outside to observe the welder at all times and be capable of putting rescue operations into effect. d. When arc welding is suspended for any substantial period of time, such as during lunch or overnight, all electrodes will be removed from the holders with the holders carefully located so that accidental contact cannot occur. The welding machines will be disconnected from the power source. e. In order to eliminate the possibility of gas escaping through leaks or improperly closed valves when gas welding or cutting, the gas and oxygen supply valves will be closed, the regulators released, the gas and oxygen lines bled, and the valves on the torch shut off when the equipment will not be used for a substantial period of time. Where practical, the torch and hose will also be removed from the confined space. f. After welding operations are completed, the welder will mark the hot metal or provide some other means of warning other workers.

Section II. SAFETY PRECAUTIONS IN OXYFUEL WELDING

or any purpose other than thatfor which they are intended. j. Do not allow flare cut sparks to hit hoses. Health Protection and Ventilation. f.
. Use oxygen and acetylene or other fuel gases with the appropriate torches and only for the purpose intended. Treat regulators with respect. Never use cylinders for rollers. or in a confined space. Always use the proper tip or nozzle. Also. c. Do not hang the torch with its hose on the regulator or cylinder valves. Do not use any lubricants on regulators or tanks. Compressed gas cylinders owned by commercial companies will not be painted regulation Army olive drab. Keep work area clean and free from hazardous materials. g. Use friction lighters or stationary pilot flames. and always operate it at the proper pressure for the particular work involved. For ventilation standards. GENERAL a. Always wear protective clothing suitable for welding or flame cutting. Store full and empty cylinders separately and mark the empty ones with “MT”. Keep a clear space between the cylinder and the work so the cylinder valves can be reached easily and quickly. regulators. The explosive mixture of acetylene and oxygen might cause personal injury or property damage when ignited. make sure the torch is not burning. release the regulators. b. e.2-6. refer to paragraph 2-4. or cylinders. l. When working in confined spaces. This information should be taken from work sheets or tables supplied with the equipment. Do not use oxygen regulators with acetylene cylinders. Use cylinders in the order received. Do not light a torch with a match or hot metal. n. k. d. sparks can travel 30 to 40 ft (9 to 12 m). Do not turn valve handle using force. In addition to the information listed in section I of this chapter. h. m. supports. and tightly close the valves. provide adequate ventilation for the dissipation of explosive gases that may be generated. the following safety precautions must be observed. Do not experiment with torches or regulators in any way. bleed the hoses. When not in use. i. When flame cutting.

(10) Open oxygen torch valve 1/4 turn. bronze. (11) Adjust to neutral flame. NOTE Use only friction type lighter or specially provided lighting device. Use mechanical exhaust at the point of welding when welding or cutting lead. manganese. chronium. Always use the following sequence and technique for lighting a torch: (1) Open acetylene cylinder valve. then the oxygen valve. (2) Close acetylene cylinder valve. r. Do not weld or flame cut on containers that have held combustibles without taking special precautions.
. or galvanized steel. brass. (8) Turn off oxygen torch valve (this will purge the oxygen line).o. (7) Screw in oxygen regulator screw to working pressure. (5) Close torch valves. Always use the following sequence and technique for shutting off a torch: (1) Close acetylene torch valve first. (4) Back off regulator adjusting valve handle until no spring tension is left. (5) Slowly open oxygen cylinder valve all the way. (2) Open acetylene torch valve 1/4 turn. q. (3) Screw in acetylene regulator adjusting valve handle to working pressure. (6) Open oxygen torch valve 1/4 turn. (4) Turn off the acetylene torch valve (this will purge the acetylene line). (3) Open torch acetylene and oxygen valves to release pressure in the regulator and hose. (9) Open acetylene torch valve 1/4 turn and light with lighter. p. zinc. cadmium. then oxygen cylinder valve.

except when cylinders are in use. Cylinders should be kept at a safe distance from the welding operation so there will be little possivility of sparks. g. Never use acetylene without reducing the pressure with a suitable pressure reducing regulator. The cylinders must be stored upright in a well ventilated. or in any are with above normal temperatures. c. Do not weld or cut in a confined space without taking special precautions. gangways. etc. dry location at least 20 ft from highly combustible materials such as oil. which may be used for grounding electrical circuits. Acetylene is a compound of carbon and hydrogen. Usually. ACETYLENE CYLINDERS CAUTION If acetylene cylinders have been stored or transported horizontally (on their sides). piping systems. Always refer to acetylene by its full name and not by the word “gas” alone. one-half turn is sufficient. They should be kept away from radiators. Before attaching the pressure regulators. or strap must be used to prevent cylinders from falling or being knocked over while in use. d. Acetylene cylinders must be handled with care to avoid damage to the valves or the safety fuse plug. f. Do not store the cylinders near radiators. Outlet valves which have become clogged with ice should be thawed with warm water. Do not use scalding water or an open flame. 2-7. layout tables. Valve protection caps must always be in place. well protected. or excelsior. Wipe off the connection seat with a clean cloth. Do not weld or flame cut into sealed container or compartment without providing vents and taking special precautions. A suitable truck. b. care must be taken not to store acetylene in areas where the temperature is in excess of 137°F (58°C). Do not stand in front of valves when opening them. Always use
. Nonsparking tools should be used when changing fittings on cylinders of flammable gases. Be sure the regulator tension screw is released before opening the cylinder valve. furnaces. which may cause the safety fuse plug in the cylinder to blow out. handtight. Storage areas should be located away from elevators. a. or other places where there is danger of cylinders being knocked over or damaged by falling objects. or flames reaching them. Do not open the valve more than one and one-half turns. Never use acetylene at pressures in excess of 15 psi. chain. In tropical climates.. e. Heat will increase the pressure. stand cylinders vertically (upright) for 45 minutes prior to (before) use. hot slag. paint. open each acetylene cylinder valve for an instant to blow dirt out of the nozzles. produced by the reaction of water and calcium carbide. t.s. Acetylene is very different from city or furnace gas. Always open the valve slowly to avoid strain on the regulator gage which records the cylinder pressure.

and is in good working condition. close the valve and tighten the packing nut. away from all fires and sparks. is installed properly.the special T-wrench provided for the acetylene cylinder valve. Store compressed gas cylinders in a safe place with good ventilation. and heat away from the cylinders. spray a stream of water on the cylinder to keep it cool. 2-8. l. Make sure that all gas apparatus shows UL or FM approval. p. Always refer to oxygen by its full name and not by the word “air” alone. r. however. n. Screw on protecting caps. is an asphyxiant and can produce suffocation. Make sure that all compressed gas cylinders are secured to the wall or other structural supports. Acetylene is nontoxic. Acetylene cylinders and oxygen cylinders should be kept apart. When returning empty cylinders. Higher pressure can cause an explosion. m. j. Should a leak occur around the valve stem of the cylinder. flames. it can usually be extinguished with a wet blanket. or other apparatus with similar equipment intended for oxygen. Leave this wrench on the stem of the valve tile the cylinder is in use so the acetylene can be quickly turned off in an emergency. and the valve opened slightly to permit the contents to escape. s. If these fail. Never interchange acetylene regulators. Keep cylinder caps on when not in use. h. Acetylene is a highly combustible fuel gas and great care should be taken to keep sparks. hose. it is an anesthetic and if present in great enough concentrations. k. Cylinders leaking around the safety fuse plug should be taken outdoors. o. Never test for an acetylene leak with an open flame. Handle all compressed gas with extreme care. Keep acetylene cylinders in the vertical condition. A burlap bag wet with calcium chloride solution is effective for such an emergency.
. Always turn the acetylene cylinder so the valve outlet will point away from the oxygen cylinder. If an acetylene cylinder should catch fire. see that the valves are closed to prevent escape of residual acetylene or acetone solvent.4 kPa). Never open an acetylene cylinder valve near other welding or cutting work. i. Test all joints with soapy water. OXYGEN CYLINDERS a. Never use acetylene at a pressure in excess of 15 psi (103. q.

Do not handle oxygen cylinders roughly. Wipe off the connection seat with a clean cloth.0 ft (6. Do not use oxygen to blow out pipe lines. Before attaching the pressure regulators. 566-1965. the cylinder valve should be closed and the protecting caps screwed on to prevent damage to the valve. Do not use a hammer or wrench to open the valves. Where a liquid oxygen system is to be used to supply gaseous oxygen for welding or cutting and a bulk storage system is used. Oxygen cylinders stored in outside generator houses shall be separated from the generator or carbide storage rooms by a noncombustible partition having a fire resistance rating of at least 1 hour. Oxygen cylinders shall not be stored near highly combustible material. h. When oxygen cylinders are in use or being roved. Do not stand in front of the valve when opening it.
. Oxygen cylinders in storage shall be separated from fuel gas cylinders or combustible materials (especially oil or grease) by a minimum distance of 20. open each oxygen cylinder valve for an instant to blow out dirt and foreign matter from the nozzle. When not in use. near reserve stocks of carbide and acetylene or other fuel gas cylinders. NFPA No. Be sure that the regulator tension screw is released the before opening the valve. or in an acetylene generator compartment. f. j. k. especially in an enclosed pressurized area. open the valve to the full limit to prevent leakage around the valve stem.5 m) high and having a fire-resistance rating of at least one-half hour. c. especially oil and grease. WARNING Oil or grease in the presence of oxygen will ignite violently. or any other substance likely to cause or accelerate fire. test radiators. purge tanks or containers. or striking the cylinders with heavy objects. When the oxygen cylinder is in use. care must be taken to avoid dropping.b.1 m) or by a noncombustible barrier at least 5. All oxygen cylinders with leaky valves or safety fuse plugs and discs should be set aside and marked for the attention of the supplier. i. The partition shall be without openings and shall be gastight. d. or to “dust” clothing or work. Oxygen should never be used for “air” in any way. WARNING Do not substitute oxygen for compressd air in pneumatic tools.0 ft (1. National Fire Protection Association. e. Do not tamper with or attempt to repair oxygen cylinder valves. knocking over. Open the oxygen cylinder valve slowly to prevent damage to regulator high pressure gage mechanism. g. it shall comply with the provisions of the Standard for Bulk Oxygen Systems at Consumer Sites.

including the following: (1) MAPP gas cylinders will not detonate when dented. Never interchange oxygen regulators. (4) Explosive limits of MAPP gas are low compared to acetylene. MAPP gas is a mixture of stabilized methylacetylene and propadiene. 2-9. Always use regulators on oxygen cylinders to reduce the cylinder pressure to a low working pressure. hoses. a concentration 1/340th of its lower explosive limit in air. liquid MAPP gas boils at -36 to -4°F (-54 to -20°C). MAPP GAS CYLINDERS a. MAPP gas vaporizes when the valve is opened and is difficult to detect visually.l. MAPP gas toxicity is rated very slight. (6) MAPP cylinders are easy to handle due to their light weight. m. Although the most familiar fuel gas used for cutting and welding is acetylene. If repaired when detected. (3) Liquified fuel is insensitive to shock. c. High cylinder pressure will burst the hose. MAPP gas has an obnoxious odor detectable at 100 parts per million. This causes frost-like burns when the gas contacts the skin. Repair any leaks immediately. or incinerated. dropped. but high concentrations (5000 part per million) may have an anesthetic affect. at very high concentrations (5000 parts per million and above) MAPP gas has an anesthetic effect. Proper clothing must be worn to prevent injury to personnel. b. if leaks are ignored. (5) Leaks can be detected easily by the stron smell of MAPP gas. Once released into the open air. or other apparatus with similar equipment intended for other gases. leaks pose little or no danger. MAPP gas has some advantages in safety which should be considered when choosing a process fuel gas. propane. d. Store these fuel gas cylinders in a specified. and in a vertical condition. well-ventilated area or outdoors. natural gas. and propylene are also used. f. FUEL GAS CYLINDERS a. However.
. e. However. Store liquid MAPP gas around 70°F (21°C) and under 94 psig pressure. 2-10. (2) MAPP gas can be used safely at the full cylinder pressure of 94 psig.

This fusible metal melts at about the killing point of water (212°F or 100°C). Immediately evacuate all people from the area. When the gas cylinders are in use a regulator is attached and the cylinder should be secured to prevent falling by means of chains or clamps. The best action is to put water on the cylinder to keep it cool and to keep all other acetylene cylinders in the area cool. e. Escaping fuel gas can also be a fire or explosion hazard. They should never be used as rollers. All acetylene cylinders are equipped with one or more safety relief devices filled with a low melting point metal. 2-11. An arc strike on a cylinder will damage the cylinder causing possible fracture. If fire occurs on or near an acetylene cylinder the fuse plug will melt. the valve stem. Care must be taken to protect the valve from damage or deterioration. try to put it out as quickly as possible. The major hazard of compressed gas is the possibility of sudden release of the gas by removal or breaking off of the valve. They should not be dropped or struck. Attempt to remove the burning cylinder from close proximity to other acetylene cylinders. HOSES
. Any cylinders must have their caps on. either filled or empty. or from combustible buildings. Escaping gas which is under high pressure will cause the cylinder to act as a rocket. If the fire on a cylinder is a small flame around the hose connection. Hammers or wrenches should not be used to open cylinder valves that are fitted with hand wheels. They should never be moved by electromagnetic cranes. The temperature of the cylinder should never be allowed to exceed 130°F (54°C).b. and possibly explode. The escaping acetylene may be ignited and will burn with a roaring sound. Thoroughly wetting the gloves and clothing will help protect the person approaching the cylinder. A wet glove. h. from flammable or hazardous materials. mix with air. and cylinders. When cylinders are empty they should be marked empty and the valves must be closed to prohibit contamination from entering. Cylinders should be handled with respect. or the fuse plug. i. Oxygen cylinders should be stored separately from fuel gas cylinders and separately from combustible materials. It is best to allow the gas to burn rather than to allow acetylene to escape. smashing into people and property. Store cylinders in cool. They should never be in an electric circuit so that the welding current could pass through them. c. requiring the cylinder to be condemned and discarded from service. g. or mud slapped on the flame will frequently extinguish it. In a fire situation there are special precautions that should be taken for acetylene cylinders. well-ventilated areas. d. Cylinders for portable apparatuses should be securely mounted in specially designed cylinder trucks. f. It is difficult to put out such a fire. j. Avoid getting in line with the fuse plug which might melt at any time. should have the valve closed. wet heavy cloth.

and open flames. i. Single lines. c. worn places. The size of hose should be matched to the connectors. Never force hose connections that do not fit. k. Do not leave hoses where anyone can trip over them. torch.a. SAFETY IN ARC WELDING AND CUTTING
2-12. They must be kept in good repair and should be no longer than necessary. or double multiple stranded lines are available. Hoses should be periodically inspected for burns. flying sparks. red for acetylene or fuel gas. h. grease. b. The nuts on fuel gas hoses are identified by a groove machined in the center of the nuts. or tied to the waist. d. regulators. Do not use new or stored hose lengths without first blowing them out with compressed air to eliminate talc or accumulated foreign matter which might otherwise enter and clog the torch parts. This could result in personal injury. Connections on hoses are right-handed for inert gases and oxygen. Avoid kinks and tangles. oil. f. Do not use matches to check for leaks in acetylene hose. and left-handed for fuel gases. double vulcanized. ELECTRIC CIRCUITS
. Only approved gas hoses for flame cutting or welding should be used with oxyfuel gas equipment. g. or cylinders being knocked over. Always protect hoses from being walked on or run over. Never crimp hose to shut off gases. Do not work with hoses over the shoulder. and torches. or leaks at the connections. or other pipe fitting compounds for connections on hose. The international standard calls for blue for oxygen and orange for fuel gas. Protect hoses from hot slag. Replace hoses if necessary. Repair leaks by cutting hose and inserting a brass splice. In the United States. Do not allow hoses to come in contact with oil or grease. around the legs. Do not use white lead. Do not use tape for mending. or other equipment. e. j. These will penetrate and deteriorate the rubber and constitute a hazard with oxygen. l. and black for inert gas or compressed air. m. the color green is used for oxygen. damaged connections. Make sure that hoses are securely attached to torches and regulators before using.
Section III. Examine all hoses periodically for leaks by immersing them in water while under pressure.

A shock hazard is associated with all electrical equipment. Consequently. (2) Keep hands and body insulated from both the work and the metal electrode holder. Welding generators should be located or shielded so that dust. b. the precautions listed below should always be observed. All serious trouble should be investigated by a trained electrician. Model 301. If one is being used. Defective electrode holders should be replaced and connections to the holder should be tightened. water. Although the ac and dc open circuit voltages are low compared to voltages used for lighting circuits and motor driven shop tools. Ordinary household voltage (115 V) is higher than the output voltage of a conventional arc welding machine. Motor-generator welding machines feature complete separation of the primary power and the welding circuit since the generator is mechanically connected to the electric rotor. When electric generators powered by internal combustion engines are used inside buildings or in confined areas. c. including extension lights. (1) Check the welding equipment to make certain that electrode connections and insulation on holders and cables are in good condition. Disconnect switches should be used with all power sources so that they can be disconnected from the main lines for maintenance. and all types of electrically powered machinery. Excessive heating will impair the insulation and damage the cable leads. AC/DC. or other damage. All checking should be done with the machine off or unplugged. may cause electrical shock if not properly grounded. Metal frames and cases of motor generators must be grounded since the high voltage from the main line does
. A rotorgenerator type arc welding machine must have a power ground on the machine. (3) Perform all welding operations within the rated capacity of the welding cables. 4462 York St. or other foreign matter will not enter the electrical windings or the bearings. the engine exhaust must be conducted to the outside atmosphere. Inspect the cables periodically for looseness at the joints. particularly in hot weather when the welder is sweating. d. Check the welding equipment to make sur the electrode connections and the insulation on holders and cables are in good condition. Colorado 80216. these voltages can cause severe shock. NSN 3431-00-2354728. defects due to wear. Denver. electric hand tools. WELDING MACHINES a. c. contact Castolin Institute. WARNING Welding machine. Defective or loose cables are a fire hazard. b. 2-13. e. Heliarc with inert gas attachment. Avoid standing on wet floors or coming in contact with grounded surfaces.a.

Phases of a three-phase power line must be accurately identified when paralleling transformer welding machines to ensure that the machines are on the same phase and in phase with one another. like ships. Wear dry protective covering on hands and body. i. connect the work leads together and measure the voltage between the electrode holders of the two machines. There can be no splices in the electrode cable within 10 feet (3 meters) of the electrode holder. g.come into the case. it is normal to have the work terminal of many welding machines connected to it. the metal frame and cases must be grounded to the earth. If it is double the normal open circuit voltage. This voltage should be practically zero. Do not operate the rotary switch for current settings while the machine is operating under welding current load. In transformer and rectifier type welding machines. h. Splices. Use only insulated electrode holders and cables. if used in work or electrode leads. Partially used electrodes should be removed from the holders when not in use. If one machine is connected for straight polarity and one for reverse polarity. must be insulated. Do not operate the polarity switch while the machine is operating under welding current load. Corrections must be made before welding begins. Disconnect the welding machines from the power supply when they are left unattended. or structural parts are involved. If the voltage is approximately 1-1/2 times the normal open circuit voltage it means that the machines are connected to different phases of the three phase power line. Severe burning of the switch contact surfaces will result. Precautions should be taken to see that all machines are of the same polarity when connected to a common weldment.
. Check by measuring the voltage between the electrode holders of the different machines as mentioned above. A place will be provided to hang up or lay down the holder where it will not come in contact with persons or conducting objects. It is important that the machines be connected to the proper phase and have the same polarity. the voltage between the electrode holders will be double the normal open circuit voltage. When large weldments. j. f. Stray current may cause a severe shock to the operator if he should contact the machine and a good ground. Consequent arcing at the switch will damage the contact surfaces and the flash may burn the person operating the switch. The welding electrode holders must be connected to machines with flexible cables for welding application. d. Operate the rotary switch while the machine is idling. k. it means that either the primary or secondary connections are reversed. To check. The situation can also occur with respect to direct current power sources when they are connected to a common weldment. e. The work terminal of the welding machine should not be grounded to the earth. buildings.

Suitable clothing must be worn to protect exposed skin from arc radiation. m. the safety considerations for plasma arc welding are the same as for gas tungsten arc welding. Locate welding machines where they have adequate ventilation and ventilation ports are not obstructed. safety glasses with side shields or other types of eye protection with a No. PROTECTIVE SCREENS a. b. When welding is done near other personnel. 2-14. Arc welding operations give off an intense light. 6 filter lens are recommended. screens should be used. The work clamp must be securely attached to the work before the start of the welding operation. Shielding is obtained from the hot ionized gas issuing from the orifice which may be supplemented by an auxiliary source of shielding gas.
. When welding with transferred arc current up to 5A. Plasma welding is similar in many ways to the tungsten arc process. When a pilot arc is operated continuously. Although face protection is not normally required for this current range. e. 6 filter lens. 2-15. Cleaning operations using these materials should be shielded from the arc rays of the plasma arc. which causes air to break down into ozone. c. and filler metal may or may not be supplied. c. See paragraph 2-2 e for screen design and method of use. Adequate ventilation is required during the plasma arc welding process due to the brightness of the plasma arc. b. when necessary. screens should be used to protect their eyes from the arc or reflected glare. a standard welder's helmet with proper shade of filter plate for the current being used is required. its use depends on personal preference. When welding with transferred arc currents between 5 and 15A.l. Therefore. In addition to using portable screens to protect other personnel. pressure may or may not be used. a full plastic face shield is recommended in addition to eye protection with a No. normal precautions should be used for protection against arc flash and heat burns. PLASMA ARC CUTTING AND WELDING a. d. Shielding gas may be an inert gas or a mixture of gases. to prevent drafts of air from interfering with the stability of the arc. Snap-on light-proof screens should be used to cover the windows of the welding truck to avoid detection when welding at night. The bright arc rays also cause fumes from the hydrochlorinated cleaning materials or decreasing agents to break down and form phosgene gas. At current levels over 15A. Plasma arc welding is a process in which coalescence is produced by heating with a constricted arc between an electrode and the work piece (transfer arc) or the electrode and the constricting nozzle (nontransfer arc).

Air carbon arc cutting is an arc cutting process in which metals to be cut are melted by the heat of a carbon arc and the molten metal is removed by a blast of air.
c. and oscillators should be properly grounded. the surrounding area does not reach high temperatures. Adequate eye protection should be used when observation of a high frequency discharge is required to center the electrode. h. preparing joints. This cleaning. particularly when welding metals with high copper. titanium. for root gouging of full penetration welds. zirconium. This reduces the tendency towards distortion and cracking. usually by grinding. AIR CARBON ARC CUTTING AND WELDING a. arc voltage heads. b. g. The process is widely used for back gouging. d. and since the metal is melted and removed quickly. A high velocity air jet traveling parallel to the carbon electrode strikes the molten metal puddle just behind the arc and blows the molten metal out of the immediate area. i. The process can be used to cut these materials for scrap for remelting. The air carbon arc can be used for cutting or gouging most of the common metals. and to prepare grooves for welding. insulation breakdown might cause these units to become electrically “hot” with respect to ground. Air carbon arc cutting is used when slightly ragged edges are not objectionable. Adequate ventilation should be used. Welding power should be turned off before electrodes are adjusted or replaced. or beryllium contents. If not grounded. 2-16. zinc. The process is not recommended for weld preparation for stainless steel. and other similar metals without subsequent cleaning. The air carbon arc cutting process is used to cut metal and to gouqe out defective metal. such as wire feeders.f. and removing defective metal.
. Figure 2-6 shows the operation of the process. to remove old or inferior welds. lead. must remove all of the surface carbonized material adjacent to the cut. The area of the cut is small. Accessory equipment.

5 liter/rein. This is because of extremely high currents used for the large size carbon electrodes. A high noise level is associated with air carbon arc welding. At high-current levels. At high currents with high air pressure a very loud noise occurs.) up to 50 cu ft/min. The circuit diagram for air carbon arc cutting or gouging is shown by figure 2-7. conventional welding machines with constant current are used. h. When using a constant voltage (CV) power source precautions must be taken to operate it within its rated output of current and duty cycle. and all combustible materials should be moved away from the work area.0 cu ft/min. i. The volume of compressed air required ranges from as low as 5. Metal deflection plates should be placed in front of the gouging operation. the mass of molten metal removed is quite large and will become a fire hazard if not properly contained. AC type carbon electodes must be used.e. Normally.
f. ear muffs or ear plugs must be worn by the arc cutter. The air blast of air carbon arc welding will cause the molten metal to travel a very long distance. g. Alternating current power sources having conventional drooping characteristics can also be used for special applications. SAFETY PRECAUTIONS FOR GAS SHIELDED ARC WELDING
. Constant voltage can be used with this process. Ear protection. Special heavy duty high current machines have been made specifically for the air carbon arc process.) for the largest-size carbon electrodes. (2.
Section IV. j. k. The air pressure must range from 80 to 100 psi (550 to 690 kPa). (24 liter/min.

shall be provided for control of fumes and vapors in the work area. These organic vapors should be removed from the work area before welding is begun. the ozone concentration may increase to harmful levels. Furthermore. The exposure level to ozone is reduced through good welding practices and properly designed ventilation systems.g. Avoid welding where such vapors are present. and perchloroethylene) break down under the ultra-violet radiation of an electric arc and forma toxic gas. Natural ventilation may be sufficient to reduce the hazard of exposure to nitrogen oxides during welding operations. and increased argon flow. as defined in paragraph 2-4. Gas shielded arc welding processes have certain dangers associated with them. These hazards. radioactivity from thoriated tungsten electrodes. the shielded from the air in order to obtain a high molten puddle of metal should be quality weld deposit.
. amperage. include arc gases. POTENTIAL HAZARDS When any of the welding processes are used. In shielded metal arc welding. Ozone concentration increases with the type of electrodes used. (4) Vapors of Chlorinated Solvents. Good industrial hygiene practices dictate that mechanical ventilation. carbon tetrachloride. such as those described in paragraph 2-4. trichloroethylene. shielding from the air is accomplished by surrounding the arc area with a localized gaseous atmosphere throughout the welding operation at the molten puddle area. and metal fumes. shielding from the air is accomplished by gases produced by the disintegration of the coating in the arc. (1) Ozone. as prescribed in paragraph 24.. Gases. provided all three ventilation criteria given in paragraph 2-4 are satisfied. (3) Carbon Dioxide and Carbon Monoxide. be used during welding or cutting of metals. WARNING The vapors from some chlorinated solvents (e. PROTECTIVE MEASURES a. which are either peculiar to or increased by gas shielded arc welding. Carbon dioxide is disassociated by the heat of the arc to form carbon monoxide. Also. 2-18. these solvents vaporize easily and prolonged inhalation of the vapor can be hazardous. (2) Nitrogen Oxides. such as perchloroethylene. Ultraviolet radiation from the welding or cutting arc can decompose the vapors of chlorinated hydrocarbons. Nitrogen oxide concentrations will be very high when performing gas tungsten-arc cutting of stainless steel using a 90 percent nitrogen-10 percent argon mixture. radiant energy. high concentrations have been found during experimental use of nitrogen as a shield gas. Ventilation.2-17. The hazard from inhalation of these gases will be minimal if ventilation requirements found in paragraph 2-4 are satisfied. With gas shielded arc welding. extension of arc tine. If welding is carried out in confined spaces and poorly ventilated areas.

which is painful and disabling but generally temporary. produce ultraviolet and infrared rays which have a harmful effect on the eyes and skin upon continued or repeated exposure. Do not weld in places where dust or other combustible particles are suspended in air or where explosive vapors are present. Ventilation and personal protective equipment requirements as prescribed in paragraph 2-4 shall be employed to prevent hazardous exposure. the exposure is minimal. Gas tungsten-arc welding using these electrodes may be employed with no significant hazard to the welder or other room occupants.carbon tetrachloride. Sources of the vapors can be wiping rags. and throat irritation can result when the welder is exposed to these substances. or open containers of the solvent. Containers of this kind can be made safe by following one of the methods described in paragraphs 2-22 through 2-26. nose. presumably because of the high ultraviolet radiation from arc welding and cutting. and cutting containers which are not free of combustible solids. the source of the chlorinated solvents should be located so that no solvent vapor will reach the welding or cutting area. The production of ultraviolet radiation doubles when gas-shielded arc welding is performed. The usual effect of ultraviolet is to “sunburn” the surface of the eye. Eye. c. Ultraviolet radiation may also produce the same effects on the skin as a severe sunburn. Since this decompsition can occur even at a considerable distance from the arc. b. special ventilation or protective equipment other than that specified in paragraph 2-4 is not needed for protection from exposure hazards associated with welding with thoriated tungsten electrodes. Infrared radiation has the effect of heating the tissue with which it comes in contact. Leather and WoOl clothing is preferable to cotton clothing during gas-shielded arc welding. Severe explosions and fires can result from heating. and trichloroethylene. Cotton clothing disintegrates in one day to two weeks. Electric arcs. Removal of flammable material from vessels and/or containers may be done either by steaming out or boiling. Cleaning the container is necessary in all cases before welding or cutting. Flammable and explosive substances may be present in a container because it previously held one of the following substances:
. Radioactivity from Thoriated Tungsten Electrodes. d. liquids. vapors. Generally. WARNING Do not assume that a container that has held combustibles is clean and safe until proven so by proper tests. as well as gas flames. The physiological response from exposure to metal fumes varies depending upon the metal being welded. vapor degreasers. EXPLOSION HAZARDS a. and gases. if the heat is not sufficient to cause an ordinary thermal burn. Radiant Energy. b.
Section V. Therefore. to form highly toxic substances. Metal Fumes. SAFETY PRECAUTIONS FOR WELDING AND CUTTING CONTAINERS THAT HAVE HELD COMBUSTIBLES
2-19. dusts. welding.

causing the container to explode. or other volatile liquid that releases potentially hazardous vapors at atomspheric pressure.(1) Gasoline. The explosimeter is an instrument which can quickly measure an atomsphere for concentrations of flammable gases and vapors. or a hollow area on a casting. c. silicones. It will not test for mixtures of hydrogen. and other compounds containing silicon in the test atomsphere may seriously impair the response of the instrument. b. Hollow areas can also contain oxygen-enriched air or fuel gases. acetylene. This device chemically reacts with the tetraethyl lead vapors to produce a more volatile lead compound. or other combustibles in which the oxygen content exceeds that of normal air (oxygen-enriched atomspheres). It is important to keep in mind that the explosimeter measures only flammable gases and vapors. should be given special attention prior to welding. d.. 2-20. Testing Atomspheres Contaminated with Leaded Gasoline. but will release such vapors when exposed to heat. (4) A combustible solid. heat from welding the metal can raise the temperature of the enclosed air or gas to a dangerously high pressure. Model 2A Explosimeter is a general purpose combustible gas indicator. (2) An acid that reacts with metals to produce hydrogen. hollow compartment in a welding. For example. Model 4 is designed for testing oxygen-acetylene mixtures and is calibrated for acetylene. tank. To reduce this possibility. Even though it may contain only air. When an atomsphere contaminated with lead gasoline is tested with a Model 2A Explosimeter. Cleaning the container is necessary in all cases before cutting or welding. the lead produces a solid product of combustion which. c. i. an inhibitor-filter should be inserted in place of the normal cotton filter in the instrument. may develop a coating upon the detector filament resulting in a loss of sensitivity. e. (3) A nonvolatile oil or a solid that will not release hazardous vapors at ordinary temperatures. light oil. Some of these materials rapidly “poison” the
. Any container of hollow body such as a can. silicates. an atomsphere that is indicated non-hazardous from the standpoint of fire and explosion may be toxic if inhaled by workmen for some time. upon repeated exposure. CAUTION Silanes. finely divided particles which may be present in the form of an explosive dust cloud. Model 3 Explosimeter is similar except that it is equipped with heavy duty flashback arresters which are capable of confining within the combustion chambers explosions of mixtures of hydrogen or acetylene and oxygen in excess of its normal content in air. USING THE EXPLOSIMETER a. One inhibitor-filter will provide protection for an instrument of eight hours of continuous testing. which can be hazardous when heated exposed to an arc or or flame.

When a test is made with the instrument and the inter pointer is deflected to the extreme right side of the scale and remains there. The circuit of the instrument must be balanced with air free of combustible gases or vapors surrounding the detector filament. an additional two squeezes will be required for each 10 ft (3m) of line. To test for combustible gases or vapors in an atomsphere. there will be an initial deflection of the meter pointer. Thus. This operation closes the battery circuit. The rheostat knob is held in the “OFF” position by a locking bar. If a sampling line is used. A clockwise rotation sufficient to move the meter pointer considerably above “ZERO” should be avoided as this subjects the detector filament to an excessive current and may shorten its life. add two squeezes for each 10 ft (3 m) of line. 454380 calibration test kit is available to conduct this test. (6) Aspirate sample through instrument until highest reading is obtained. If a sampling line is used. This control is a rheostat regulating the current to the Explosimeter measuring circuit. The graduations on the scale of the indicating inter are in percent of the lower explosive limit. the atmosphere under test is explosive. the point where the sample is to be taken. Five squeezes of the aspirator bulb are sufficient to flush the combustion chamber. (3) Adjust rheostat knob until meter pointer rests at “ZERO”. When such materials are even suspected to be in the atmosphere being tested. Approximately five squeezes of the bulb are sufficient to give maximum deflection. The meter pointer may move rapidly upscale and then return to point below “ZERO”. the instrument must be checked frequently (at least after 5 tests). or drop directly helm “ZERO”. immediately replace the filament and the inlet filter. If the instrument reads low on the test gas.detector filament so that it will not function properly. This reading indicates the concentration of combustible gases or vapors in the sample. (2) Flush fresh air through the instrument. The MSA Explosimeter is set in its proper operating condition by the adjustment of a single control. (5) Readjust meter pointer to "ZERO" if necessary by turning rheostat knob. Part no. a deflection of the meter pointer between zero and 100 percent shins how closely the atmosphere being tested approaches the minimum concentration required for the explosion. (4) Place end of sampling line at. Because of unequal heating or circuit elements.
. or transport the Model 2A Explosimeter to. Operation Instructions. This bar must be lifted before the knob can be turned from “OFF” position. operate the Model 2A Explosimeter as follows: (1) Lift the left end of the rheostat knob “ON-OFF” bar and turn the rheostat knob one quarter turn clockwise. Clockwise rotation of the rheostat knob causes the meter pointer to move up scale. e.

(7) To turn instrument off: Rotate rheostat knob counterclockwise until arrow on knob points to “OFF”. If this is not practical. Then. enabling rich concentrations of gas to be compared. if the meter pointer moves first to the right and then to the left of the scale. The instrument may be used to locate the position of the leak by utilizing this bar hole pressure. immediately aspirate fresh air through the sampling line or directly into the instrument. such as in testing bar holes in the ground adjacent to a leak in a buried gas pipe. it is necessary that the instrument be operated in fresh air and the gaseous sample delivered to the instrument through the sampling line in order to permit a comparison of a series of samples beyond the normal range of the instrument to determine which sample contains the highest concentration of combustible gases. or in following the purging of a closed vessel that has contained f flammable gases or vapors. When it is necessary to estimate or compare concentrations of combustible gases above the lower explosive limit a dilution tube may be employed. it is an indication that the concentration of flammable gas or vapor in the sample is above the upper explosive limit. the balance adjustment should be made at 3-minute internals during the first ten minutes of testing and every 10 minutes thereafter. Observe the time required for this pressure to force gas through the instrument sampling line. The tube also makes it possible to folbw the progress of purging operation when an atomsphere of combustibles is being replaced with inert gases. For those tests in which concentrations of combustible gases in excess of liner explosive limit concentrations (100 percent on instrument inter) are to be compared. The locking bar will drop into position in its slot indicating that the rheostat is in the “OFF” position. This condition usually occurs near a large leak. f. A probe tube equipped with a plug for sealing off
. a special air-dilution tube must be used. and on continued aspiration quickly returns to a position within the scale range or below “ZERO”. Such gas-air mixtures are considered unsafe. Special Sampling Applications (1) Dilution tube. In sane instances when bar holes are drilled to locate pipe line leaks. (2) Pressure testing bar holes. In all tests made with the dilution tube attached to the instrument. It is expected that the gas pressure will be greatest in the bar hole nearest the leak. Such dilution tubes are available in 10:1 and 20:1 ratios of air to sample. it is an indication that the concentration of flammable gases or vapors may be above the upper explosive limit.If the meter pointer moves rapidly across the scale. The meter scale is red above 60 to indicate that gas concentrations within that range are very nearly explosive. a group of holes all containing pure gas may be found. To verify this. NOTE When possible. the bridge circuit balance should be checked before each test. See paragraph 2-20 f (1).

Observe the time at which this is done. Other nonferrous metals and alloys should be tested for reactivity prior to cleaning. d. c. The bar hole showing the shortest time will have the greatest pressure. and insoluble in water. replace the aspirator bulb and flush out the probe line for the next test. including all internal piping. e. When the upward deflection of the meter pointer starts. Do not use any tools which may spark and cause flammable vapors to ignite. These materials may be decomposed by heat or radiation from welding or cutting to form phosgene. or using a nonferrous chain as a srubber. Determine the time required for the gas to pass through the probe line. hammering with a nonferrous mallet. and standpipes. turn off the instrument. If the substance previously held by the container is not known. Cleaning the container is necessary in all cases before welding or cutting. toxic. a. Adjust the rheostat until the meter pointer rests on “ZERO”. If practical. The probe tube is now inserted in the bar hole and sealed off with the plug. Aluminum and aluminum alloys should not be cleaned with caustic soda or cleaners having a pH above 10. NOTE No container should be considered clean or safe until proven so by tests.
. Empty and drain the container thoroughly. Disconnect or remove from the vicinity of the container all sources of ignition before starting cleaning. move the container into the open. make sure the room is well ventilated so that flammable vapors may be carried away. Pressure developed in the bar hole will force gas through the sampling line to the instrument. 2-21. when cleaning. Cleaning should be done by personnel familiar with the characteristics of the contents. indicated by an upward deflection of the meter pointer as the gas reaches the detector chamber. Identify the material for which the container was used and determine its flammability and toxicity characteristics.the bar hole into which it is inserted is required. Removal of scale and sediment may be facilitated by scraping. When indoors. assure that the substance is flammable. PREPARING THE CONTAINER FOR CLEANING CAUTION Do not use chlorinated hydrocarbons. traps. aspirate fresh air through the Explosimeter and unscrew the aspirator bulb coupling. such as trichloroethylene or carbon tetrachloride. To remove the flow regulating orifice from the instrument. Dispose of the residue before starting to weld or cut. as they may react chemically. b. Personnel cleaning the container must be protected against harmful exposure.

regardless of which comparment is be welded or cut. c. wear approved respiratory protective equipment.
. Various methods of cleaning containers which have held flammable liquids are listed in this section. g. d. This cleaning may be supplemental by filling the container with water or an inert gas both before and during such work. Other nonferrous metals and alloys should be investigated for reactivity prior to cleaning.12 kg per 1)) and rinse it sufficiently to ensure that the inside surface is thoroughly finished. When handling dry caustic soda or soda ash. long sleeves.f. a. 2-22. and gloves. the automotive exhaust and steam cleaning methods are considered by military personnel to be the safest and easiest methods of purging these containers. It is very important for the safety of personnel to completely clean all tanks and containers which have held volatile or flammable liquids. Safety precautions cannot be overemphasized because of the dangers involved when these items are not thoroughly purged prior to the application of heat. Drain the solution and rinse the container again with clean water. METHODS OF PRECLEANING CONTAINERS WHICH HAVE HELD FLAMMABLE LIQUIDS a. hot water. Treat each compartment in a container in the same manner. Fill the container at least 25 percent full with a solution of hot soda or detergent (1 lb per gal of water (0. AUTOMOTIVE EXHAUST METHOD OF CLEANING WARNING Head and eye protection. The automotive exhaust method of cleaning should be conducted only in well-ventilated areas to ensure levels of toxic exhaust gases are kept below hazardous levels. General. 2-23. b. rubber gloves. Completely drain the container of all fluid. Fire resistant hand pads or gloves must be worn when handling hot drums. Cleaning a container that has held combustibles is necessary in all cases before any welding or cutting is done. Accepted Methods of Cleaning. especially open flame. b. Open all inlets and outlets of the container. and aprons must be worn when handling steam. CAUTION Aluminum and aluminum alloys should not be cleaned with caustic soda or cleaners having a pH above 10. as they may react chemically. However. and caustic solutions. boots.

or soda ash (1 lb per gal of water (0.e. boots. and gloves.12 kg per 1)) and agitate it sufficiently to ensure that the inside surfaces are thoroughly flushed. Control the steam pressure by a valve ahead of the hose. Use steam under low pressure and a hose of at least 3/4-in. Using a flexible tube or hose. as they may react chemically. If a metal nozzle is used at the outlet end. and aprons must be worn when handling steam. Close all openings in the container except the drain and filling connection or vent. 2-24. detergent. Allow the gases to circulate through the container for 30 minutes. repeat cleaning procedure. wear approved respiratory protective equipment. Fire resistant hand pads or gloves must be worn when handling hot drums. it should be made of nonsparkinq material and should be electrically connected to the container. The container. a.05 mm) diameter. rubber gloves. (19. b. Drain the solution thoroughly. The automotive exhaust method of cleaning should be conducted only in well-ventilated areas to ensure levels of toxic exhaust gases are kept below hazardous levels. g. long sleeves. Close the container openings. in turn. f. If the vapor concentration is in excess of 14 percent of the lower limit of flammability. e. Other nonferrous metals. reopen the container and test with a combustible gas indicator. STEAM METHOD OF CLEANING WARNING Head and eye protection. d. Disconnect the tube from the container and use compressed air (minimum of 50 psi (345 kPa)) to blow out all gases. and alloys should be investigated for reactivity prior to cleaning. Fill the container at least 25 percent full with a solution of hot soda. NOTE Do not use soda ash solution on aluminum. When handling dry caustic soda or soda ash. Make sure there are sufficient openings to allow the gases to flow through the container. CAUTION Aluminum and aluminum alloys should not be cleaned with caustic soda or cleaners having a pH above 10. direct a stream of exhaust gases into the container. Use damp wood flour or similar material for sealing cracks or other damaged sections. h. c. should be grounded to prevent an accumulation of static electricity. and caustic solutions. hot water.
. After 15 minutes. Completely drain the container of all fluid.

use a mirror to reflect light into the container. HOT CHEMICAL SOLUTION METHOD OF OF CLEANING WARNING Wear head and eye protection. WATER METHOD OF CLEANING a. long sleeves. b. preferably through the drain. water. It may take several hours to heat the container to such a temperature that steam will flow freely from the outlet of the container. to protect against burns. rubber gloves. position it so the condensate will drain from the same opening the steam inserted into. Water-soluble substances can be removed by repeatedlv filling and draining the container with water. (3) Thoroughly flush the inside of the container with hot. and caustic solutions. acetone. When handling dry caustic soda or soda ash. If inspection shows that it is not clean. Diluted acid frequently reacts with metal to produce hydrogen. repeat steps (1) through (4) above and inspect again. preferably boiling. The procedure for the steam method of cleaning is as follows: (1) Blow steam into the container. Wear fire resistant hand pads or gloves to handle hot drums.) (2) Continue steaming until the container is free from odor and the metal parts are hot enough to permit steam vapors to flow freely out of the container vent or similar opening. If the vapor concentration is in excess of 14 percent of the lower limit of flammbility. Water-soluble acids. boots. such as boots. etc. wear suitable clothing. (Use a nonmetal electric lantern or flashlight which is suitable for inspection of locations where flammable vapors are present. To do this. repeat the cleaning procedure. When a container has only one opening. or other weather conditions may condense the steam as fast as it is introduced. (4) Drain the container. (5) Inspect the inside of the container to see if it is clean. hot water. (When steam or hot water is used to clean a container. hood. reopen the container and test with a combustible gas indicator.. 2-26. and alcohol can be removed in this manner. and gloves. When the original container substance is not readily water-soluble. for a period of time to be governed by the condition or nature of the flammable substance previously held by the container. CAUTION
. care must be taken to ensure that all traces of the acid are removed.f. wear approved respiratory protective equipment. In 15 minutes. it must be treated by the steam method or hot chemical solution method. and aprons when handling steam. Do not set a definite time limit for steaming containers since rain. extreme cold. 2-25.) (6) Close the container openings.

Aluminum and aluminum alloys should not be cleaned with caustic soda or cleaners having a pH above 10, as they may react chemically. Other nonferrous metals and alloys should be investigated for reactivity prior to cleaning. a. The chemicals generally used in this method are trisodium phosphate (strong washing powder) or a commercial caustic cleaning compound dissolved in water to a concentration of 2 to 4 oz (57 to 113 g) of chemical per gallon of water. b. The procedure for the hot chemical solution method of cleaning is as follows: (1) Close all container openings except the drain and filling connection or vent. Use damp wood flour or similar material for sealing cracks or other damaged sections. (2) Fill the container to overflowing with water, preferably letting the water in through the drains. If there is no drain, flush the container by inserting the hose through the filling connection or vent. Lead the hose to the bottom of the container to get agitation from the bottom upward. This causes any remaining liquid, scum, or sludge to be carried upward and out of the container. (3) Drain the container thoroughly. (4) Completely dissolve the amount of chemical required in a small amount of hot or boiling water and pour this solution into the container. Then fill the container with water. (5) Make a steam connection to the container either through the drain connection or by a pipe entering through the filling connection or vent. Lead the steam to the bottom of the container. Admit steam into the chemical solution and maintain the solution at a temperature of 170 to 180°F (77 to 82°C). At intervals during the steaming, add enough water to permit overflying of any volatile liquid, scum, or sludge that may have collected at the top. Continue steaming to the point where no appreciable amount of volatile liquid, scum, or sludge appears at the top of the container. (6) Drain the container. (7) Inspect the inside of the container as described in paragraph 2-24 f (5). If it is not clean, repeat steps (4) thru (6) above and inspect again. (8) Close the container openings. In 15 minutes, test the gas concentration in the container as described in paragraph 2-24 f (6). c. If steaming facilities for heating the chemical solution are not available, a less effective method is the use of a cold water solution with the amount of cleaning compound increased to about 6 oz (170 g) per gal of water. It will help if the solution is agitated by rolling the container or by blowing air through the solution by means of an air line inserted near the bottom of the container.

d. Another method used to clean the container is to fill it 25 percent full with cleaning solution and clean thoroughly, then introduce low pressure steam into the container, allowing it to vent through openings. Continue to flow steam through the container for several hours. 2-27. MARKING OF SAFE CONTAINERS After cleaning and testing to ensure that a container is safe for welding and cutting, stencil or tag it. The stencil or tag must include a phrase, such as “safe for welding and cutting,” the signature of the person so certifying, and the date. 2-28. FILLING TREATMENT It is desirable to fill the container with water during welding or cutting as a supplement to any of the cleaning methods (see fig. 2-8). Where this added precaution is taken, place the container so that it can be kept find to within a few inches of the point where the work is to be done. Make sure the space above the water level is vented so the heated air can escape from the container.

2-29. PREPARING THE CLEAN CONTAINER FOR WELDING OR CUTTING--INERT GAS TREATMENT a. General. Inert gas may be used as a supplement to any of the cleaning methods and as an alternative to the water filling treatment. If sufficient inert gas is mixed with flammable gases and vapors, the mixture will come non-flammable. A continuous flow of steam may also be used. The steam will reduce the air concentration and make the air flammable gas mixture too lean to burn. Permissible inert gases include carbon dioxide and nitrogen. b. Carbon Dioxide and Nitrogen. (1) When carbon dioxide is used, a minimum concentration of 50 percent is required, except when the falmmable vapor is principally hydrogen, carbon monoxide, or acetylene. In these cases, a minimum concentration of 80 percent carbon dioxide is required. Carbon dioxide is heavier than air, and during welding or cutting operations will tend to remain in containers having a top opening.

(2) When nitrogen is used, the concentrations should be at least 10 percent greater than those specified for carbon dioxide. (3) Do not use carbon monoxide. c. Procedure. The procedure for inert gas, carbon dioxide, or nitrogen treatment is as follows: (1) Close all openings in the container except the filling connection and vent. Use damp wood flour or similar material for sealing cracks or other damaged sections. (2) Position the container so that the spot to be welded or cut is on top. Then fill it with as much water as possible. (3) Calculate the volume of the space above the water level and add enough inert gas to meet the minimum concentration for nonflammability. This will usually require a greater volume of gas than the calculated minimum, since the inert gas may tend to flow out of the vent after displacing only part of the previously contained gases or vapors. (4) Introduce the inert gas, carbon dioxide, or nitrogen from the cylinder through the container drain at about 5 psi (34.5 kPa). If the drain connection cannot be used, introduce the inert gas through the filling opening or vent. Extend the hose to the bottom of the container or to the water level so that the flammable gases are forced out of the container. (5) If using solid carbon dioxide, crush and distribute it evenly over the greatest possible area to obtain a rapid formation of gas. d. Precautions When Using Carbon Dioxide. Avoid bodily contact with solid carbon dioxide, which may produce “burns”. Avoid breathing large amounts of carbon dioxide since it may act as a respiratory stimulant, and, in sufficient quantities, can act as an asphyxiant. e. Inert Gas Concentration. Determine whether enough inert gas is present using a combustible gas indicator instrument. The inert gas concentration must be maintained during the entire welding or cutting operation. Take steps to maintain a high inert gas concentration during the entire welding or cutting operation by one of the following methods: (1) If gas is supplied from cylinders, continue to pass the gas into the container. (2) If carbon dioxide is used in solid form, add small amounts of crushed solid carbon dioxide at intervals to generate more carbon dioxide gas.

WARNING Welding polyurethane foam-filled parts can produce toxic gases. Welding should not be attempted on parts filled with polyurethane foam. If repair by welding is necessary, the foam must be removed from the heat-affected area, including the residue, prior to welding. a. General. Welding polyurethane foam filled parts is a hazardous procedure. The hazard to the worker is due to the toxic gases generated by the thermal breakdown of the polyurethane foam. The gases that evolve from the burning foam depend on the amount of oxygen available. Combustion products of polyurethane foam in a clean, hot fire with adequate oxygen available are carbon dioxide, water vapor, and varying amounts of nitrogen oxides, carbon monoxide, and traces of hydrogen cyanide. Thermal decomposition of polyurethanes associated with restricted amounts of oxygen as in the case of many welding operations results in different gases being produced. There are increased amounts of carbon monoxide, various aldehydes, isocyanates and cyanides, and small amounts of phosgene, all of which have varying degrees of toxicity. b. Safety Precautions. (1) It is strongly recommended that welding on polyurethane foam filled parts not be performed. If repair is necessary, the foam must be removed from the heataffected zone. In addition, all residue must be cleaned from the metal prior to welding. (2) Several assemblies of the M113 and M113A1 family of vehicles should not be welded prior to removal of polyurethane foam and thorough cleaning.

CHAPTER 3 PRINT READING AND WELDING SYMBOLS

Section I. PRINT READING
3-1. GENERAL a. Drawings. Drawing or sketching is a universal language used to convey all necessary information to the individual who will fabricate or assemble an object. Prints are also used to illustrate how various equipment is operated, maintained, repaired, or lubricated. The original drawings for prints are made either by directly drawing or tracing a drawing on a translucent tracing paper or cloth using waterproof (India) ink or a special pencil. The original drawing is referred to as a tracing or master copy. b. Reproduction Methods. Various methods of reproduction have been developed which will produce prints of different colors from the master copy. (1) One of the first processes devised to reproduce a tracing produced white lines on a blue background, hence the term "blueprints". (2) A patented paper identified as "BW" paper produces prints with black lines on a white background. (3) The ammonia process, or "Ozalids", produces prints with either black, blue, or maroon lines on a white background. (4) Vandyke paper produces a white line on a dark brown background. (5) Other reproduction methods are the mimeograph machine, ditto machine, and photostatic process. 3-2. PARTS OF A DRAWING a. Title Block. The title block contains the drawing number and all the information required to identify the part or assembly represented. Approved military prints will include the name and address of the Government Agency or organization preparing the drawing, the scale, the drafting record, authentication, and the date. b. Revision Block. Each drawing has a revision block which is usually located in the upper right corner. All changes to the drawing are noted in this block. Changes are dated and identified by a number or letter. If a revision block is not used, a revised drawing may be shown by the addition of a letter to the original number.

c. Drawing Number. All drawings are identified by a drawing number. If a print has more than one sheet and each sheet has the same number, this information is included in the number block, indicating the sheet number and the number of sheets in the series. d. Reference Numbers and Dash Numbers. Reference numbers that appear in the title block refer to other print numbers. When more than one detail is shown on a drawing, dashes and numbers are frequently used. If two parts are to be shown in one detail drawing, both prints will have the same drawing number plus a dash and an individual number such as 7873102-1 and 7873102-2. e. Scale. The scale of the print is indicated in one of the spaces within the title block. It indicates the size of the drawing as compared with the actual size of the part. Never measure a drawing-use dimensions. The print may have been reduced in size from the original drawing. f. Bill of Material. A special block or box on the drawing may contain a list of necessary stock to make an assembly. It also indicates the type of stock, size, and specific amount required. 3-3. CONSTRUCTION LINES a. Full Lines (A, fig. 3-1). Full lines represent the visible edges or outlines of an object.

b. Hidden Lines (A, fig. 3-1). Hidden lines are made of short dashes which represent hidden edges of an object. c. Center Lines (B, fig. 3-1). Center lines are made with alternating short and long dashes. A line through the center of an object is called a center line. d. Cutting Plane Lines (B, fig. 3-1). Cutting plane lines are dashed lines, generally of the same width as the full lines, extending through the area being cut. Short solid wing lines at each end of the cutting line project at 90 degrees to that line and end in arrowheads which point in the direction of viewing. Capital letters or numerals are placed just beyond the points of the arrows to designate the section. e. Dimension Lines (A, fig. 3-1). Dimension lines are fine full lines ending in arrowheads. They are used to indicate the measured distance between two points. f. Extension Lines (A, fig. 3-1). Extension lines are fine lines from the outside edges or intermediate points of a drawn object. They indicate the limits of dimension lines. g. Break Lines (C, fig. 3-1). Break lines are used to show a break in a drawing and are used when it is desired to increase the scale of a drawing of uniform cross section while showing the true size by dimension lines. There are two kinds of break lines: short break and long break. Short break lines are usually heavy, wavy, semiparallel lines cutting off the object outline across a uniform section. Long break lines are long dash parallel lines with each long dash in the line connected to the next by a "2" or sharp wave line.

Section II. WELD AND WELDING SYMBOLS
3-4. GENERAL Welding cannot take its proper place as an engineering tool unless means are provided for conveying the information from the designer to the workmen. Welding symbols provide the means of placing complete welding information on drawings. The scheme for symbolic representation of welds on engineering drawings used in this manual is consistent with the "third angle" method of projection. This is the method predominantly used in the United States. The joint is the basis of reference for welding symbols. The reference line of the welding symbol (fig. 3-2) is used to designate the type of weld to be made, its location, dimensions, extent, contour, and other supplementary information. Any welded joint indicated by a symbol will always have an arrow side and an other side. Accordingly, the terms arrow side, other side, and both sides are used herein to locate the weld with respect to the joint.

The tail of the symbol is used for designating the welding and cutting processes as well as the welding specifications, procedures, or the supplementary information to be used in making the weld. If a welder knows the size and type of weld, he has only part of the information necessary for making the weld. The process, identification of filler metal that is to be used, whether or not peening or root chipping is required, and other pertinent data must be related to the welder. The notation to be placed in the tail of the symbol indicating these data is to be establish by each user. If notations are not used, the tail of the symbol may be omitted. 3-5. ELMENTS OF A WELDING SYMBOL A distinction is made between the terms "weld symbol" and "welding symbol". The weld symbol (fig. 3-3) indicates the desired type of weld. The welding symbol (fig. 3-2) is a method of representing the weld symbol on drawings. The assembled "welding symbol" consists of the following eight elements, or any of these elements as necessary: reference line, arrow, basic weld symbols, dimensions and other data, supplementary symbols, finish symbols, tail, and specification, process, or other reference. The locations of welding symbol elements with respect to each other are shown in figure 3-2.

3-6. BASIC WELD SYMBOLS a. General. Weld symbols are used to indicate the welding processes used in metal joining operations, whether the weld is localized or "all around", whether it is a shop or field weld, and the contour of welds. These basic weld symbols are summarized below and illustrated in figure 3-3. b. Arc and Gas Weld Symbols. See figure 3-3. c. Resistance Weld Symbols. See figure 3-3. d. Brazing, Forge, Thermit, Induction, and Flow Weld Symbols. (1) These welds are indicated by using a process or specification reference in the tail of the welding symbol as shown in figure 3-4.

(2) When the use of a definite process is required (fig. 3-5), the process may be indicated by one or more of the letter designations shown in tables 3-1 and 3-2.

NOTE Letter designations have not been assigned to arc spot, resistance spot, arc seam, resistance seam, and projection welding since the weld symbols used are adequate.

(3) When no specification, process, or other symbol, the tail may be omitted (fig. 3-6). reference is used with a welding

e. Other Common Weld Symbols. Figures 3-7 and 3-8 illustrate the weld-all-around and field weld symbol, and resistance spot and resistance seam welds.

f. Supplementary Symbols. These symbols are used in many welding processes in congestion with welding symbols and are used as shown in figure 3-3. 3-7. LOCATION SIGNIFICANCE OF ARROW a. Fillet, Groove, Flange, Flash, and Upset welding symbols. For these symbols, the arrow connects the welding symbol reference line to one side of the joint and this side shall be considered the arrow side of the joint (fig. 3-9). The side opposite the arrow side is considered the other side of the joint (fig. 3-10).

b. Plug, Slot, Arc Spot, Arc Seam, Resistance Spot, Resistance Seam, and Projection Welding Symbols. For these symbols, the arrow connects the welding symbol reference line to the outer surface of one member of the joint at the center line of the desired weld. The member to which the arrow points is considered the arrow side member. The other member of the joint shall be considered the other side member (fig. 3-11).

c. Near Side. When a joint is depicted by a single line on the drawing and the arrow of a welding symbol is directed to this line, the arrow side of the joint is considered as the near side of the joint, in accordance with the usual conventions of drafting (fig. 3-12 and 3-13).

d. Near Member. When a joint is depicted as an area parallel to the plane of projection in a drawing and the arrow of a welding symbol is directed to that area, the arrow side member of the joint is considered as the near member of the joint, in accordance with the usual conventions of drafting (fig. 3-11). 3-8. LOCATION OF THE WELD WITH RESPECT TO JOINT a. Arrow Side. Welds on the arrow side of the joint are shown by placing the weld symbol on the side of the reference line toward the reader (fig. 3-14).

b. Other Side. Welds on the other side of the joint are shown by placing the weld symbol on the side of the reference line away from the reader (fig. 3-15).

c. Both Sides. Welds on both sides of the joint are shown by placing weld symbols on both sides of the reference line, toward and away from the reader (fig. 3-16).

d. No Side Significance. Resistance spot, resistance seam, flash, weld symbols have no arrow side or other side significance in themselves, although supplementary symbols used in conjunction with these symbols may have such significance. For example, the flush contour symbol (fig. 3-3) is used in conjunction with the spot and seam symbols (fig. 3-17) to show that the exposed surface of one member of the joint is to be flush. Resistance spot, resistance seam, flash, and upset weld symbols shall be centered on the reference line (fig. 3-17).

3-9. REFERENCES AND GENERAL NOTES a. Symbols With References. When a specification, process, or other reference is used with a welding symbol, the reference is placed in the tail (fig. 3-4).

b. Symbols Without References. Symbols may be used without specification, process, or other references when: (1) A note similar to the following appears on the drawing: "Unless otherwise designated, all welds are to be made in accordance with specification no...." (2) The welding procedure to be used is described elsewhere, such as in shop instructions and process sheets. c. General Notes. General notes similar to the following may be placed on a drawing to provide detailed information pertaining to the predominant welds. This information need not be repeated on the symbols: (1) "Unless otherwise indicated, all fillet welds are 5/16 in. (0.80 cm) size." (2) "Unless otherwise indicated, root openings for all groove welds are 3/16 in. (0.48 cm)." d. Process Indication. When use of a definite process is required, the process may be indicated by the letter designations listed in tables 3-1 and 3-2 (fig. 3-5). e. Symbol Without a Tail. When no specification, process, or other reference is used with a welding symbol, the tail may be omitted (fig. 3-6). 3-10. WELD-ALL-AROUND AND FIELD WELD SYMBOLS a. Welds extending completely around a joint are indicated by mans of the weld-all-around symbol (fig. 3-7). Welds that are completely around a joint which includes more than one type of weld, indicated by a combination weld symbol, are also depicted by the weld-all-around symbol. Welds completely around a joint in which the metal intersections at the points of welding are in more than one plane are also indicated by the weld-all-around symbol. b. Field welds are welds not made in a shop or at the place of initial construction and are indicated by means of the field weld symbol (fig. 3-7). 3-11. EXTENT OF WELDING DENOTED BY SYMBOLS a. Abrupt Changes. Symbols apply between abrupt changes in the direction of the welding or to the extent of hatching of dimension lines, except when the weld-all-around symbol (fig. 3-3) is used. b. Hidden Joints. Welding on hidden joints may be covered when the welding is the same as that of the visible joint. The drawing indicates the presence of hidden members. If the welding on the hidden joint is different from that of the visible joint, specific information for the welding of both must be given.

3-12. LOCATION OF WELD SYMBOLS a. Weld symbols, except resistance spot and resistance seam, must be shown only on the welding symbol reference line and not on the lines of the drawing. b. Resistance spot and resistance seam weld symbols may be placed directly at the locations of the desired welds (fig. 3-8). 3-13. USE OF INCH, DEGREE, AND POUND MARKS NOTE Inch marks are used for indicating the diameter of arc spot, resistance spot, and circular projection welds, and the width of arc seam and resistance seam welds when such welds are specified by decimal dimensions. In general, inch, degree, and pound marks may or may not be used on welding symbols, as desired. 3-14. CONSTRUCTION OF SYMBOLS a. Fillet, bevel and J-groove, flare bevel groove, and corner flange symbols shall be shown with the perpendicular leg always to the left (fig. 3-18).

b. In a bevel or J-groove weld symbol, the arrow shall point with a definite break toward the member which is to be chamfered (fig. 3-19). In cases where the member to be chamfered is obvious, the break in the arrow may be omitted.

c. Information on welding symbols shall be placed to read from left to right along the reference line in accordance with the usual conventions of drafting (fig. 3-20).

3-22). a symbol shall be shown for each weld (fig 3-21). or other data with a reference on the welding symbol according to location specifications given in para 3-7 (fig.
.d.
f. 3-23). For joints having more than one weld. The letters CP in the tail of the arrow indicate a complete penetration weld regardless of the type of weld or joint preparation (fig. the weld shall be shown by a cross section. When the basic weld symbols are inadequate to indicate the desired weld. detail.
e.

the weld-all-around symbol must be placed at the junction of the arrow line and reference line for each operation to which it applies (fig. The field weld symbol may also be used in this manner. 3-24). Two or more reference lines may be used to indicate a sequence of operations. 3-25). Subsequent operations must be shown sequentially on other reference lines (fig.
. 3-26). Test information may be shown on a second or third line away from the arrow (fig. When required.g. The first operation must be shown on the reference line nearest the arrow. Additional reference lines may also be used to show data supplementary to welding symbol information included on the reference line nearest the arrow.

3-27). both welds must be dimensioned (C or D. 3-27). When fillet welds are indicated on both sides of a joint and a general note governing the dimensions of the welds appears on the drawing. both must be dimensioned (D. neither weld need be dimensioned.
b. fig. (2) When the welds differ in dimensions. fig. 3-27). The size of a fillet weld must of a fillet weld be shown to the left of the weld symbol (A. one or both may be dimensioned (B or C. fig. the dimensions are indicated as follows: (1) When both welds have the same dimensions. if the dimensions of one or both welds differ from the dimensions given in the general note.3-15. SIZE OF FILLET WELDS a. When fillet welds are indicated on both sides of a joint and no general note governing the dimensions of the welds appears on the drawing. 3-27). 3-16. c. fig. FILLET WELDS Dimensions of fillet welds must be shown on the same side of the reference line as the weld symbol (A. 3-27).
. fig. However.

3-18. b. Weld orientation is not shown by the symbol and must be shown on the drawing when necessary (E. c. the deposited fillet weld size must not be less than the size shown on the drawing. 3-27). Fillet welding extending beyond abrupt changes in the direction of the welding must be indicated by additional arrows pointing to each section of the joint to be welded (fig. 3-28). 3-17. d. fig. Unless otherwise indicated. LENGTH OF FILLET WELDS a. no length dimension need be shown on the welding symbol. must be shown to the right of the weld symbol (A through D. 3-29) except when the weld-all-around symbol is used.b. EXTENT OF FILLET WELDING a. The length of a fillet weld. fig. The size the fillet weld with unequal legs must be shown in parentheses to left of the weld symbol. 3-27). Use one type of hatching (with or without definite lines) to show the extent of fillet welding graphically. when indicated on the welding symbol. b.
. When penetration for a given root opening is specified. c. the inspection method for determining penetration depth must be included in the applicable specification. Specific lengths of fillet welding may be indicated by symbols in conjunction with dimension lines (fig. When fillet welding extends for the full distance between abrupt changes in the direction of the welding.

Dimensions of staggered intermittent fillet welding must be shown on both sides of the reference line as shown in figure 3-31.
Unless otherwise specified. The pitch of intermittent fillet welding shall be shown to the right of the length dimension (A.3-19. staggered intermittent fillet welds on both sides shall be symmetrically spaced as in figure 3-32.
d. b. fig 3-27). Chain intermittent fillet welds shall be opposite each other (fig. 3-30). Dimensions of chain intermittent fillet welding must be shown on both sides of the reference line. The pitch (center-to-center spacing) of intermittent fillet welding shall be shown as the distance between centers of increments on one side of the joint. DIMENSIONING OF INTERMITTENT FILLET WELDING a.
. c.

the symbol indicates that increments are located at the ends of the dimensioned length.3-20. Separate symbols must be used for intermittent and continuous fillet welding when the two are combined along one side of the joint (fig. the symbol indicates that spaces equal to the pitch minus the length of one increment shall be left at the ends of the dimensioned length.
. 3-21. 3-28). convex. 3-33). fig. When intermittent fillet welding is used by itself. or concave faced without recourse to any method of finishing must be shown by adding the flush. TERMINATION OF INTERMITTENT FILLET WELDING a. convex. Fillet welds that are to be welded approximately flat. in accordance with the location specifications given in paragraph 3-7 (A. or concave contour symbol to the weld symbol. When intermittent fillet welding is used between continuous fillet welding. SURFACE CONTOUR OF FILLET WELDS a. c. b.

e. Neither the plug weld symbol nor the slot weld symbol may be used to designate fillet welds in holes. c. NOTE Finish symbols used here indicate the method of finishing (" c" = chiping. 3-33). 3-22. Fillet welds that are to be mechanically finished to a concave contour must be shown by adding both the concave contour symbol and the user's standard finish symbol to the weld symbol in accordance with location specification given in paragraph 3-7. Fillet welds that are to be mechanically finished to a convex contour shall be shown by adding both the convex contour symbol and the user's standard finish symbol to the weld symbol. fig. "M" = machining). PLUG AND SLOT WELDING SYMBOLS a. in accordance with location specifications given in paragraph 3-7 (C.
. in accordance with location specifications given in paragraph 3-7 (B. 3-33). fig. In cases where the angle between fusion faces is such that the identification of the type of weld and the proper weld symbol is in question. Holes or slots in the arrow side member of a joint for plug or slot welding must be indicated by placing the weld symbol on the side of the reference line toward the reader (A. "H" = hammering. the detail of the desired joint and weld configuration must be shown on the drawing. not the degree of finish. fig. General. 3-11). Holes or slots in the other side member of a joint shall be indicated by placing the weld symbol on the side of the reference line away from the reader (B. d.b. fig. Arrow Side and Other Side Indication of Plug and Slot Welds. b. Fillet welds that are to be made flat faced by mechanical means must be shown by adding both the flush contour symbol and the user's standard finish symbol to the weld symbol. 3-11). "G" = grinding.

3-34). the depth of filling shall be shown in inches inside the weld symbol (B.
. when not the user's standard. Surface Contour of Plug Welds and Slot Welds. e.
d. Depth of filling of plug and slot welds shall be completed unless otherwise indicated. Dimensions of plug welds must be shown on the same side of the reference line as the weld symbol. Plug Weld Dimensions. fig. Depth of Filling of Plug and Slot Welds. must be shown either above or below the weld symbol (A and C. Included angle of countersink of plug welds must be the user's standard unless otherwise indicated. Plug welds that are to be welded flush by mechanical means must be shown by adding both the flush contour symbol and the user's standard finish symbol to the weld symbol (fig. 3-34). fig. Plug welds that are to be welded approximately flush without recourse to any method of finishing must be shown by adding the finish contour symbol to the weld symbol (fig.c. The pitch (center-to-center spacing) of plug welds shall be shown to the right of the weld symbol. 3-36). When the depth of filling is less than complete. The size of a weld must be shown to the left of the weld symbol. Included angle of countersink. 3-35).

Slot Weld Dimensions. 3-23. width. Details of Slot Welds. in accordance with its location in relation to the reference line. and location of slot welds cannot be shown on the welding symbols. The spot weld symbol.
g. fig. fig. The process reference is indicated in the tail of the welding symbol. Size of Arc Spot and Arc Seam Welds. 3-33). with or without inch marks. to the left of the weld symbol (A. 3-37). Arc seam weld size shall be designated as the width of the weld. in accordance with location specifications given in paragraph 3-7 (D. Then projection welding is to be used. (2) The size of arc spot welds must be designated as the diameter of the weld. Dimensions of slot welds must be shown on the same side of the reference line as the weld symbol (fig. General. Dimensions must be shown on the same side of the reference line as the symbol or on either side when the symbol is located astride the reference line and has no arrow side or other side significance. Dimensions will be expressed in fractions or in decimals in hundredths of an inch and shall be shown. Length.f. included angle of countersink. 3-38).
. The spot weld symbol must be centered above or below the. orientation. b. This data must be shown on the drawing or by a detail with a reference to it on the welding symbol. reference line. (1) These welds may be dimensioned by either size or strength. the spot weld symbol shall be used with the projection welding process reference in the tail of the welding symbol. ARC SPOT AND ARC SEAM WELDS a. spacing. may or may not have arrow side or other side significance.

Strength is shown to the left of the weld symbol (B. fig. the length of arc seam welds. 3-39).
(3) A group of spot welds may be located on a drawing by intersecting center lines.
(2) When a definite number of arc spot welds is desired in a certain joint. 3-40). the number must be shown in parentheses either above or below the weld symbol (fig. (2) When spot welding or arc seam welding extends for the full distance between abrupt changes in the direction of welding.
. must be shown to the right of the weld symbol (C. strength is designated in pounds per linear inch. 3-38). In arc seam welds. (1) When arc spot welding extends less than the distance between abrupt changes in the direction of welding or less than the full length of the joint. d. when indicated. 3-38). fig. The arrows point to at least one of the centerlines passing through each weld location. Extent and Number of Arc Spot Welds and Arc Seam Welds. Spacing of Arc Spot and Arc Seam Welds. the extent must be dimensioned (fig. no length dimension need be shown on the welding symbol. (1) The pitch (center-to-center spacing) of arc spot welds and. c.(3) The strength of arc spot welds must be designated as the minimum accept-able shear strength in pounds or newtons per spot.

(1) Dimensions of groove welds must be shown on the same side of the reference line as the weld symbol (fig. When the exposed surface of one member of an arc spot or arc seam welded joint is to be flush. 3-41) in the same manner as that for fillet welds (para 3-21).
. 3-24. 3-42).
f. extent. and location of arc seam welds cannot be shown on the welding symbols. that surface must be indicated by adding the flush contour symbol (fig.e. 3-43). orientation. This data must be shown on the drawing.
(2) When no general note governing the dimensions of double groove welds appears. dimensions shall be shown as follows: (a) When both welds have the same dimensions. Spacing. Details of Arc Seam Welds. one or both may be dimensioned (fig. General. Flush Arc Spot and Arc Seam Welded Joints. GROOVE WELDS a.

(3) When a general note governing the dimensions of groove welds appears. b. (1) The size of groove welds shall be shown to the left of the weld symbol (fig. 3-44). 3-44). neither symbol need be dimensioned. Size of Groove Welds.(b) When the welds differ in dimensions. 3-45). fig.
. 3-44). the dimensions of double groove welds shall be indicated as follows: (a) If the dimensions of both welds are as indicated in the note. both shall be dimensioned (fig. (2) Specifications for groove welds with no specified root penetration are shown as follows: (a) The size of single groove and symmetrical double groove welds which extend completely through the member or members being joined need not be shown on the welding symbol (A and B. both welds shall be dimensioned (fig. (b) When the dimensions of one or both welds differ from the dimensions given in the general note.

(b) The size of groove welds which extend only partly through the member members being joined must be shown on the welding symbol (A and B. fig.
(3) The groove welds. The size of square groove welds must be indicated by showing only the root penetration. The depth of chamfering and the root penetration must read in that order from left to right along the reference line (A and B. 3-47).
. groove angle.
(4) The size of flare groove welds is considered to extend only to the tangent points as indicated by dimension lines (fig. 3-46). except square must be indicated by showing the depth of chamfering and the root penetration separated by a plus mark and placed to the left of the weld symbol. 3-48).
c. groove radii. and root faces of the U and J groove welds are the user's standard unless otherwise indicated. fig. size of groove welds with specified root penetration. Groove Dimensions (1) Root opening.

The contour symbols for groove welds (F. (c) Groove radii and root faces of U and J groove welds are shown by a cross section. with a reference to it on the welding symbol. the weld symbols are as follows: (a) Root opening is shown inside the weld symbol (fig. 3-42). 3-49). 3-22).
e.
. in accordance with location specifications given in paragraph 3-7 (fig. 3-51) are indicated in the same manner as that for fillet welds (para 3-21). 3-50). in accordance with the location specifications given in paragraph 3-7 (fig. fig. Surface Contour of Groove Welds. Back and Backing Welds. 3-52).
(1) Groove welds that are to be welded approximately flush without recourse to any method of finishing shall be shown by adding the flush contour symbol to the weld symbol. Bead-type back and backing welds of single-groove welds shall be shown by means of the back or backing weld symbol (fig. or other data.
(b) Groove angle of groove welds is shown outside the weld symbol (fig. d.(2) When the user's standard is not used. detail.

(2) Back or backing welds of single-groove welds must be shown by placing a back or backing weld symbol on the side of the reference line opposite the groove weld symbol (fig. (3) Dimensions of back or backing welds should not be shown on the welding symbol. If it is desired to specify these dimensions. in accordance with the location specifications given in paragraph 3-7 (fig. b. 3-55) for back or backing welds are indicated in the same manner as that for fillet welds (para 3-21). 3-53). BACK OR BACKING WELDS a. they must be shown on the drawing. 3-54).
. 3-50) must be used to indicate bead-type back or backing welds of single-groove welds.(2) Groove welds that are to be made flush by mechanical means shall be shown by adding the flush contour symbol and the user's standard finish symbol to the weld symbol. 3-50). Surface Contour of Back or Backing Welds. General. in accordance with the location specifications given in para 3-7 (fig.
3-25. (1) The back or backing weld symbol (fig. The contour symbols (fig.
(3) Groove welds that are to be mechanically finished to a convex contour shall be shown by adding both the convex contour symbol and the user's standard finish symbol to the weld symbol.

MELT-THRU WELDS a. they must be shown on the drawing. The contour symbols for melt-thru welds are indicated in the same manner as that for fillet welds (fig.
(2) Melt-thru welds shall be shown by placing the melt-thru weld symbol on the side of the reference line opposite the groove weld. 3-56).
3-27. Surface Contour of Melt-thru Welds. or corner weld symbol (fig. (3) Dimensions of melt-thru welds should rot be shown on the welding symbol. flange. (1) The melt-thru symbol shall be used where at least 100 percent joint penetration of the weld through the material is required in welds made from one side only (fig. General. General. 356). If it is desired to specify these dimensions.3-26. SURFACING WELDS a.
. b. tee. 3-57).

no dimension.
. 3-58). c.(1) The surfacing weld symbol shall be used to indicate surfaces built up by welding (fig. other than size. need be shown on the welding symbol. When the entire area of a plane or curved surface is to be built up by welding. General. Size of Built-up Surfaces. The size (height) of a surface built up by welding shall be indicated by showing the minimum height of the weld deposit to the left of the weld symbol. If only a portion of the area of a plane or curved surface is to be built up by welding. 3-59). This symbol shall be drawn on the side of the reference line toward the reader and the arrow shall point clearly to the surface on which the weld is to be deposited. The dimensions shall always be on the same side of the reference line as the weld symbol (fig. These symbols have no arrow or other side significance. and orientation of the area to be built up shall be indicated on the drawing. 3-28. the extent. Location. FLANGE WELDS a. no size dimension need be shown on the welding symbol. and Orientation of Surfaces Built up by Welding. When no specific height of weld deposit is desired. 3-58). whether built up by single-or multiple-pass surfacing welds. Extent. b.
(2) The surfacing weld symbol does not indicate the welding of a joint and thus has no arrow or other side significance. (1) The following welding symbols are used for light gage metal joints involving the flaring or flanging of the edges to be joined (fig. location.

The radius and height must read in that order from left to right along the reference line (C.
. a break in the arrow is required to show which member is flanged (fig. fig. 3-59). (1) Dimensions of flange welds are shown on the same side of the reference line as the weld symbol.(2) Edge flange welds shall be shown by the edge flange weld symbol (A. separated by a plus mark. fig. 3-59). and placed to the left of the weld symbol. 3-59). In cases where the corner flange joint is not detailed. Dimensions of Flange Welds. fig. (3) Corner flange welds shall be shown by the corner flange weld symbol (B. 3-59). (2) The radius and the height above the point of tangency must be indicated by showing the radius and height. b.

(2) The strength of resistance spot welds is designated as the minimum acceptable shear strength in pounds per spot and must be shown to the left of the weld symbol (fig. (1) The pitch of resistance spot welds shall be shown to the right of the weld symbol (fig.(3) The size (thickness) of flange welds must be shown by a dimension placed outward of the flange dimensions (C. Spacing of Resistance Spot Welds. although supplementary symbols used in con-junction with them may have such significance. the same symbol shall be used as for the two outer pieces. regardless of the number of pieces inserted. Dimensions may be shown on either side of the reference line. Resistance spot weld symbols (fig. RESISTANCE SPOT WELDS a. fig. If specification of this dimension is desired. to the left of the weld symbol (fig. General.
c. (4) Root opening of flange welds are not shown on the welding symbol. 3-61). Size of Resistance Spot Welds. 3-29. 3-3) have no arrow or other side significance in themselves. Resistance spot weld symbols shall be centered on the reference line. it must be shown on the drawing. with or without inch marks. 3-59).
. b. For flange welds in which one or more pieces are inserted between the two outer pieces. 3-62). c. Resistance spot welds are dimensioned by either size or strength as follows: (1) The size of resistance spot welds is designated as the diameter of the weld expressed in fractions or in decimals in hundredths of an inch and must be shown. Multiple-Joint Flange Welds. 3-60).

d. (fig. the spacing is shown by using dimension lines. the number must be shown in parentheses either above or below the weld symbol (fig.
. Flush Resistance Spot Welding Joints. Number of Resistance Spot Welds. 3-3) to the weld symbol. When the exposed surface of one member of a resistance spot welded joint is to be flush.
e. 3-65) in accordance with location specifications given in paragraph 3-7. 364). that surface shall be indicated by adding the flush contour symbol (fig. When a definite number of welds is desired in a certain joint. the extent must be dimensioned (fig. (3) When resistance spot welding extends less than the distance between abrupt changes in the direction of the welding or less than the full length of the joint. 3-63).(2) When the symbols are shown directly on the drawing.

3-66). although supplementary symbols used in injunction with them may have such significance.
. (2) Dimensions of resistance seam welds may be shown on either side of the reference line. Resistance seam welds must be dimensioned by either size or strength as follows: (1) The size of resistance seam welds must be designated as the width of the weld expressed in fractions or in decimals in hundredths of an inch and shall be shown. Length of Resistance Seam Welds.3-30.
c. (1) The length of a resistance seam weld. must be shown to the right of the welding symbol (fig. to the left of the weld symbol (fig. 3-68).
(2) The strength of resistance seam welds must be designated as the minimum acceptable shear strength in pounds per linear inch and must be shown to the left of the weld symbol (fig. RESISTANCE SEAM WELDS a. 3-67). Size of Resistance Seam Welds. General. b. (1) Resistance seam weld symbols have no arrow or other side significance in themselves. Resistance seam weld symbols must be centered on the reference line. with or without inch marks. when indicated on the welding symbol.

3-70). 3-79). The pitch of intermittent resistance seam welding shall be designated as the distance between centers of the weld increments and must be shown to the right of the length dimension (fig. When used between continuous resistance seam welding. the symbol indicates that increments are located at the ends of the dimensioned length.
d. 3-3) to the weld symbol. that surface shall be indicated by adding the flush contour symbol (fig. observing the usual location significance (fig. Flush Projection Welded Joints.
e. When intermittent resistance seam welding is used by itself. Termination of Intermittent Resistance Seam Welding. the symbol indicates that spaces equal to the pitch minus the length of one increment are left at the ends of the dimensional length. f.
. When the exposed surface of one member of a projection welded joint is to be made flush. 3-69). Separate symbols must be used for intermittent and continuous resistance seam welding when the two are combined. the extent must be dimensioned (fig. (3) When resistance seam welding extends less than the distance between abrupt changes in the direction of the welding or less than the full length of the joint.(2) When resistance seam welding extends for the full distance between abrupt changes in the direction of the welding. no length dimension need be shown on the welding symbol. Pitch of Resistance Seam Welds.

(2) Embossments on the arrow side member of a joint for projection welding shall be indicated by placing the weld symbol on the side of the reference line toward the reader (fig. 3-73). (1) When using projection welding. The spot weld symbol must be centered on the reference line.3-31.
.
(3) Embossment on the other side member of a joint for projection welding shall be indicated by placing the weld symbol on the -side of the reference line away from the reader (fig. PROJECTION WELDS a. 3-72). the spot weld symbol must be used with the projection welding process reference in the tail of the welding symbol. General.

fig. Number of Projection Welds. (1) Projection welds must be dimensioned by strength. b. 3-76). 3-75).(4) Proportions of projections must be shown by a detail or other suitable means. Spacing of Projection Welds.
c. to the left of the weld symbol (fig. (2) The size of circular projection welds shall be designated as the diameter of the weld expressed in fractions or in decimals in hundredths of an inch and shall be shown. the number shall be shown in parentheses (F. When a definite number of projection welds is desired in a certain joint.
. Circular projection welds may be dimensioned by size.
d. Size of Projection Welds. The pitch of projection welds shall be shown to the right of the weld symbol (fig. (5) Dimensions of projection welds must be shown on the same side of the reference line as the weld symbol. 3-77). with or without inch marks.
(3) The strength of projection welds shall be designated as the minimum acceptable shear strength in pounds per weld and shall be shown to the left of the weld symbol (fig. 3-74).

Flush Resistance Seam Welded Joints. the extent shall be dimensioned (fig. When the exposed surface of one member of a resistance seam welded joint is to be flush. The contour symbols (fig. b. 371). Extent of Projection Welding. although supplementary symbols used in conjunction with then may have such significance. that surface shall be indicated by adding the flush contour symbol (fig.
. observing the usual location significance (fig. Dimensions need not be shown on the welding symbol.
3-32.e. 3-3) to the weld symbol. FLASH OR UPSET WELDS a. 3-78).
f. When the projection welding extends less than the distance between abrupt changes in the direction of the welding or less than the full length of the joint. 3-3) for flash or upset welds (fig. Flash or upset weld symbols have no arrow side or other side significance in themselves. The weld symbols for flash or upset welding must be centered on the reference line. Surface Contour of Flash or Upset Welds. 3-80) are indicated in the same manner as that for fillet welds (paragraph 3-21). General.

.

E. B. d. Corner Joint. JOINT TYPES Welds are made at the junction of the various pieces that make up the weldment. The junctions of parts. C. sheet. pipes. are defined as the location where two or more nembers are to be joined. The five basic types of welding joints are listed below. A joint between two overlapping members. Edge Joint. L. Lap Joint. castings. b. Butt Joint.
. forgings. A joint between two members lying approximately in the same plane.
a.CHAPTER 4 JOINT DESIGN AND PREPARATION OF METALS
4-1. A joint between the edges of two or more parallel or mainly parallel members. Parts being joined to produce the weldment may be in the form of rolled plate. or billets. shapes. A joint between two members located approximately at right angles to each other in the form of an angle. or joints. c.

. Purpose. T. it is necessary to combine the joint types with weld types to produce weld joints for joining the separate members. Weld joints are designed to transfer the stresses between the members of the joint and throughout the weldment. 4-2. WELD JOINT DESIGN AND PREPARATION a. Table 4-1 shows the welds applicable to the basic joints. Each weld type cannot always be combined with each joint type to make a weld joint. A joint between two members located approximately at right angles to each other in the form of a T. Forces and loads are introduced at different points and are transmitted to different areas throughout the weldment. WELD JOINTS In order to produce weldments .e.
4-3. The type of loading and service of the weldment have a great bearing on the joint design required. Tee Joint.

NOTE When joints are subjected to dynamic loading. Specific information on welding carbon and low alloy metals may be found in chapter 7. thermal cutting. Strength. The rating of the joint is based on the percentage of weld metal depth to the total joint. or machining. or must.
. The joint surface should not be nicked or gouged since nicks and gouges may interfere with the welding operation. scale. the weld joint must be very efficient. The aluminum or aluminum alloy will react chemically with these types of cleaners. Suitable solvents or light grinding can be used for cleaning. the joint surfaces must be cleared of all foreign materials such as paint. d.b. Such services require full-penetration welds. These weld joints are prepared either by flame cutting or mechanically by machining or grinding. CAUTION Aluminum and aluminum alloys should not be cleaned with caustic soda or strong cleaner with a pH above 10. The cross-sectional area is a measurement of the amount or weight of weld metal that must be used to make the joint. paragraph 7-10. depending on the joint details. e. Before welding. This is more important if the weldment is sub jetted to cold-temperature service. (1) Mild and low alloy steels are generally stronger than the materials being joined. and impact leads. Design. special precautions must be taken to ensure the welding heat does not cancel the heat treatment of the base metal. The weld joint must be designed so that its cross-sectional area is the minimum possible. dirt. (1) A full penetration joint has weld metal throughout the entire cross section of the weld joint. c. Categories. (1) Carbon and low alloy joint design and preparation. a 50 percent partial penetration joint would have weld metal halfway through the joint. reversing loads. causing it to revert to its lower strength adjacent to the weld. i. Designs that increase stresses by the use of partial-penetration joints are not acceptable for this type of service. (2) When welding high-alloy or heat-treated materials. (2) A partial penetration joint has an unfused area and the weld does not completely penetrate the joint. Joints may be prepared by shearing. but also on the strength of the weld metal. The strength of weld joints depends not only on the size of the weld. Other nonferrous metals and alloys should be investigated prior to using these cleaners to determine their reactivity.. All weld joints can be classified into two basic categories: full penetration joints and partial penetration joints.

paragraph 7-14. Cleaning may be done with suitable solvents (e. Specific information regarding welding stainless steel alloy metals may he found in chapter 7. Figure 4-2 illustrates several types of inaccessible welds. WELD ACCESSIBILITY The weld joint must be accessible to the welder using the process that is employed.
. paragraph 7-17. Specific information regarding welding aluminum and aluminum alloy metals may be found in chapter 7.(2) Aluminum and aluminum alloy joint design and preparation. such as paint.. Care should be taken to avoid nicking or gouging the joint surface since such flaws can interfere with the welding operation. or oxide. These weld joints are prepared either by plasma arc cutting or by machining or grinding. 4-4. or etching can be used. Weld joints are often designed for welds that cannot be made. acetone or alcohol) or light grinding. light grinding. or oxides. Before welding. Weld joint designs often unintentionally require welds that cannot be made. g. Check your design to avoid these and similar errors. Before welding. scale. depending on the alloy. the joint surfaces must be cleared of all foreign materials such as paint. solvent cleaning. The joint surfaces should not be nicked or gouged since nicks and gouges may interfere with welding operations. dirt. scale. (3) Stainless steel alloy joint design and preparation. the joint surfaces must be cleaned of all foreign material. dirt.

a. Oxygen is obtained from a number of cylinders manifolded and equipped with a master regulator. GENERAL The equipment used for oxyacetylene welding consists of a source of oxygen and a source of acetylene from a portable or stationary outfit. 5-2. 5-2). and wrenches to operate the various connections on the cylinders. OXYACETYLENE WELDING EQUIPMENT
5-1. STATIONARY WELDING EQUIPMENT Stationay welding equipment is installed where welding operations are conducted in a fixed location. and torches.
. a method to light the torch. The oxygen is supplied to the welding stations through a pipe line equipped with station outlets (fig. Other equipment requirements include suitable goggles for eye protection. along with a cutting attachment or a separate cutting torch. regulators. 51). Oxygen and acetylene are provided in the welding area as outlined below. The regulator and manifold control the pressure and the flow together (fig. gloves to protect the hands. Oxygen.CHAPTER 5 WELDING AND CUTTING EQUIPMENT
Section I.

.

b. Acetylene is obtained either from acetylene cylinders set up as shown in figure 5-3. or an acetylene generator (fig. Acetylene.
. 5-4). The acetylene is supplied to the welding stations through a pipe line equipped with station outlets as shown in figure 5-2.

.

The trucks are equipped with a platform to support two large size cylinders. welded to the frame. PORTABLE WELDING EQUIPMENT The portable oxyacetylene welding outfit consists of an oxygen cylinder and an acetylene cylinder with attached valves. generated by the action of calcium carbide. goggles. and water in a generating unit. Acetylene is a fuel gas composed of carbon and hydrogen (C2H2). The cylinders are secured by chains attached to the truck frame. gloves.
5-4.
.5-3. ACETYLENE GENERATOR NOTE Acetylene generator equipment is not a standard included in this manual for information only. and necessary wrenches. but has a distinctive odor that can be easily detected. 5-5). fluxes. This equipment may be temporarily secured on the floor or mounted on an all welded steel truck. and hoses (fig. regulators. a. a gray stonelike substance. gauges. A metal toolbox. provides storage space for torch tips. Acetylene is colorless.

Under pressure of 29. cone tip temperatures of approximately 6300°F (3482°C). In the operation of the generator. acetylene can be safely burned with oxygen for heating.b. it becomes unstable. CAUTION Although acetylene is nontoxic. and a slight shock can cause it to explode spontaneously. CAUTION Since considerable heat is given off during the reaction. the output for this load is approximately 300 cu ft per hour for 4. if compressed to 15 psi (103. and possibly explode. welding. Acetylene burns in the air with an intensely hot. Heat or shock can cause acetylene under pressure to explode. containing from 2 to 80 percent acetylene by volume. precautions must be taken to prevent excessive pressures in the generator which might cause fires or explosions. A single rated 300-lb generator uses 300 lb of calcium carbide and 300 gal.4 psi (203) kPa). produces an oxyacetylene flame with inner. manufactured by the reaction of water and calcium carbide. A sludge. The generator shown in figure 5–4 is a commonly used commercial type. However. and if present in a sufficiently high concentration.4 kPa). d. a. for an oxidizing flame. is an asphyxiant in that it replaces oxygen and can produce suffocation. will explode when ignited. the calcium carbide is added to the water through a hopper mechanism at a rate which will maintain a working pressure of approximately 15 psi (103. 5850°F (3232°C) for a neutral flame. Mixtures of acetylene and air. This amount of material will generate 4. Avoid exposing filled cylinders to heat.5 cu ft of acetylene per pound. yellow. consisting of hydrated or slaked lime. c. Avoid striking the cylinder against other objects and creating sparks. can break down from heat or shock. Acetylene. acetylene becomes self-explosive.4 kPa). and 5700°F (3149°C) for a carburizing flame. To avoid shock when transporting
. ACETYLENE CYLINDERS WARNING Acetylene. settles in the bottom of the generator and is removed by means of a sludge outlet. and cutting purposes. smoky flame.5 hours. luminous. stored in a free state under pressure greater than 15 psi (103. 5-5. flammable gas composed of carbon and hydrogen. when burned with oxygen. radiators. furnaces.5 hours. e. Although acetylene is stable under low pressure. or sparks (from a torch). It is slightly lighter than air. b. it is an anesthetic. A pressure regulator is a built-in part of this equipment. open fires. of water.4 kPa). A double rated generator uses 300 lb of finer sized calcium carbide fed through a special hopper and will deliver 600 cu ft of acetylene per hour for 2. with suitable welding equipment and proper precautions. Acetylene is a colorless.

Acetone. or about 275 cu ft per hour. For welding purposes. the volume of acetone increases as it absorbs the acetylene. or portland cement. charcoal. a colorless. or slide them on their sides. acetylene is contained in three common cylinders with capacities of 1.cylinders.1 cu ft per hour are required. Acetylene can be compressed into cylinders when dissolved in acetone at pressures up to 250 psi (1724 kPa). In order to decrease the size of the open spaces in the cylinder. To prevent drawing off of acetone and consequent impairment of weld quality and damage to the welding equipment. The porous material acts as a large sponge which absorbs the acetone. is added to the cylinder until about 40 percent of the porous material is saturated. c. which then absorbs the acetylene.1 cu ft per hour. do not drag. decreases in volume. or 32. corn pith. Acetylene must not be drawn off in volumes greater than 1/7 of the cylinder’s rated capacity. the cylinder manifold system must be used. When more than 32.
CAUTION Do not fill acetylene cylinders at a rate greater than 1/7 of their rated capacity. acetylene cylinders (fig.
. and 300 cu ft. being a gas. roll. flammable liquid. while acetylene. 100. In this process. d. 5-6) are filled with porous materials such as balsa wood. 60. do not draw acetylene from a cylinder at continuous rates in volumes greater than 1/7 of the rated capacity of the cylinder.

The regulator inlet connection gland fits against the face of the threaded cylinder connection. The liquid air process is by far the most widely used to produce oxygen. g. 5-6. are then further purified and compressed into cylinders for use. General.e. and the corrosion of aluminum are all due to the action of atmospheric oxygen. Oxygen is a colorless. having been separated. tasteless. odorless gas that is slightly heavier than air. when used with oxygen. These stems can be fitted with a cylinder wrench and opened or closed when the cylinder is in use.
. oxygen is one of the most common elements. The plug hole is too small to permit a flame to burn back into the cylinder if escaping acetylene is ignited. the plug will melt and permit the acetylene to escape before dangerous pressures can be developed. The atmosphere is made up of approximately 21 parts of oxygen and 78 parts of nitrogen. air is compressed and cooled to a point where the gases become liquid. Acetylene cylinders are equipped with safety plugs (fig. produces the highest flame temperature of any of the fuel gases. A protective metal cap (fig. The brass acetylene cylinder valves have squared stainless steel valve stems. (1) In the liquid air process. the cylinder should be marked and set aside for return to the manufacturer. It is nonflammable but will support combustion with other elements. It also has the most concentrated flame. Oxygen is obtained commercially either by the liquid air process or by the electrolytic process. known as oxidation. b. but produces less gross heat of combustion than the liquid petroleum gases and the synthetic gases. Whenever the threads on the valve connections are damaged to a degree that will prevent proper assembly to the regulator. Acetylene. In its free state. f. 5-6) screws onto the valve to prevent damage during shipment or storage. Production of Oxygen. 5-6) which have a small hole through the center. discoloration of copper. or releases at 500 psi (3448 kPa). and the union nut draws the two surfaces together. This hole is filled with a metal alloy which melts at approximately 212°F (100°C). As the temperature of the liquid air rises. nitrogen in a gaseous form is given off first. h. using a soap solution. WARNING Acetylene which may accumulate in a storage room or in a confined space is a fire arid explosion hazard. OXYGEN AND ITS PRODUCTION a. for leakage at the valves and safety fuse plugs. Rusting of ferrous metals. These gases. When a cylinder is overheated. The outlet of the valve is threaded for connection to an acetylene pressure regulator by means of a union nut. the remainder being rare gases. All acetylene cylinders should be checked. since its boiling point is lower than that of liquid oxygen.

It is made of steel and has a capacity of 220 cu ft at a pressure of 2000 psi (13. and other hose apparatus. A typical oxygen cylinder is shown in figure 5-7. and is especially dangerous in the presence of oil and grease. regulators. and must be periodically tested thereafter. oxygen cylinders undergo extensive testing prior to their release for work.790 kPa) and a temperature of 70°F (21°C). water is broken down into hydrogen and oxygen by the passage of an electric current. including the cylinder. a removable metal cap for the protection of the valve. Oxygen should never be used in any air tools or for any of the purposes for which compressed air is normally used. valves. Oxygen cylinders and apparatus should not be handled with oily hands or oily gloves. Oil and grease in the presence of oxygen may spontaneously ignite and burn violently or explode. Each gas is collected and compressed into cylinders for use.
. never as air. OXYGEN CYLINDER CAUTION Always refer to oxygen as oxygen. 5-7. and a low melting point safety fuse plug and disk. Attached equipment provided by the oxygen supplier consists of an outlet valve. Because of their high pressure. Combustibles should be kept away from oxygen. Pure oxygen will support and accelerate combustion of almost any material. The cylinder is fabricated from a single plate of high grade steel so that it will have no seams and is heat treated to achieve maximum strength.(2) In the electrolytic process. The oxygen collects at the positive terminal and the hydrogen at the negative terminal.

The single stage oxygen regulator reduces the cylinder pressure of a gas to a working pressure in one step. b. a valve seat to close off the nozzle. Single Stage Oxygen Regulator. Pressure gauges are provided to show the pressure in the cylinder or pipe line and the working pressure. acetylene.5-8. which must be reduced to a working pressure of 1 to 25 psi (6. Regulators reduce pressure and control the flow of gases from the cylinders. OXYGEN AND ACETYLENE REGULATORS a.
. General. and balancing springs. The gases compressed in oxygen and acetylene cylinders are held at pressures too high for oxyacetylene welding. The pressure of acetylene in an acetylene cylinder can be as high as 250 psi (1724 kPa). The pressure in an oxygen cylinder can be as high as 2200 psi (15. NOTE The regulators for oxygen.90 to 172. Check valves must be installed between the torch hoses and the regulator to prevent flashback through the regulator. The single stage oxygen regulator mechanism (fig. and liquid petroleum fuel gases are of different construction. They must be used only for the gas for which they were designed. Most regulators in use are either the single stage or the two stage type. Some types have a relief valve and an inlet filter to exclude dust and dirt. 5-8) has a nozzle through which the high pressure gas passes. A gas pressure regulator will automatically deliver a constant volume of gas to the torch at the adjusted working pressure.169 kPa).38 kPa).

The low or working pressure gauge. is graduated from 0 to 500 psi. (1) The regulator consists of a flexible diaphragm. which is on the inlet side of the regulator.NOTE In operation. (2) The oxygen enters the regulator through the high pressure inlet connection and passes through a glass wool filter. Operation of Single Stage Oxygen Regulator. the working pressure falls as the cylinder pressure falls. which is on the outlet side of the regulator. and an adjusting screw. The oxygen regulator controls and reduces the oxygen pressure from any standard commercial oxygen cylinder containing pressures up to 3000 psi. which compensates for the pressure of the gas against the diaphragm. Pressure is applied to the adjusting spring by turning the adjusting screw. The high pressure gauge. which controls a needle valve between the high pressure zone and the working zone. is not raised until the adjusting screw is turned in. The seat. a compression spring. which bears down on the rubber
. which removes dust and dirt. For this reason. c. The needle valve is on the side of the diaphragm exposed to high gas pressure while the compression spring and adjusting screw are on the opposite side in a zone vented to the atmosphere. which occurs gradually as gas is withdrawn. which closes off the nozzle. the working pressure must be adjusted at intervals during welding operations when using a single stage oxygen regulator. is graduated from 0 to 3000 psi.

The diaphragm presses downward on the stirrup and overcomes the pressure on the compensating spring.
e. On the low pressure side the pressure is reduced from intermediate pressure to work pressure. 5–9) is similar in operation to the one stage regulator. When the stirrup is forced downward. the pressure is reduced from cylinder pressure to intermediate pressure.4 kPa) for acetylene and approximately 200 psi (1379 kPa) for oxygen. Acetylene Regulator. acetylene manifold. the working pressure is held constant. Oxygen is then allowed to flow into the low pressure chamber of the regulator. (3) Regulators used at stations to which gases are piped from an oxygen manifold. Because of the two stage pressure control. The two stage oxygen regulator (fig. the passage through the nozzle is open.
. and pressure adjustment during welding operations is not required. but reduces pressure in two steps. On the high pressure side. or acetylene generator have only one low pressure gage because the pipe line pressures are usually set at 15 psi (103.diaphragm. A certain set pressure must be maintained in the low pressure chamber of the regulator so that oxygen will continue to be forced through the orifices of the torch. This pressure is indicated on the working pressure gage of the regulator. even if the torch needle valve is open. The oxygen then passes through the regulator outlet and the hose to the torch. and depends on the position of the regulator adjusting screw. Pressure is increased by turning the adjusting screw to the right and decreased by turning this screw to the left.

stainless steel.5 kPa). The welding tips may or may not have separate injectors designed integrally with each tip. In addition. the other for acetylene.895 kPa). b. The torch also has two needle valves. is graduated from 0 to 500 psi (3447. OXYACETYLENE WELDING TORCH a. General. and a mixing head.
. The torch consists of a handle or body which contains the hose connections for the oxygen and the fuel gas.4 kPa). one for adjusting the flew of oxygen and one for acetylene.5 kPa). inlet nipples for the attachment of hoses. The acetylene regulator design is generally the same as that of the oxygen regulator. 5-10). It also controls the volume of these gases burning at the welding tip. and the equal pressure type. Acetylene should not be used at pressures exceeding 15 psi (103. The oxyacetylene welding torch is used to mix oxygen and acetylene in definite proportions. This regulator controls the acetylene pressure from any standard commercial cylinder containing pressures up to 500 psi (3447. There are two general types of welding torches. copper-nickel alloy. one for oxygen.4 kPa). the low pressure or injector type.CAUTION Acetylene should never be used at pressures exceeding 15 psi (103. is graduated from 0 to 30 psi (207 kPa). The high pressure gage. 5-9. A jet of high pressure oxygen is used to produce a suction effect to draw in the required amount of acetylene. on the outlet side of the regulator. a tip. see paragraph 5-10. (1) In the low pressure or injector type (fig. on the inlet side of the regulator. The tubes and handle are of seamless hard brass. The low pressure gage. For a description and the different sized tips. which produces the required type of flame. Types of Torches. the acetylene pressure is less than 1 psi (6. Any change in oxygen flow will produce relative change in acetylene flow so that the proportion of the two gases remains constant. there are two tubes. This is accomplished by designing the mixer in the torch to operate on the injector principle. and a handle. but will not withstand such high pressures.

(2) The equal pressure torch (fig. 5-11) is designed to operate with equal pressures for the oxygen and acetylene. 5-10 and 5-11) are made of hard drawn electrolytic or 95 percent copper and 5 percent tellurium. the torch is less susceptible to flashbacks.895 to 103. These tip sizes are designated by numbers which are
. and since equal pressures are used for each gas. The diameters of the tip orifices differ in order to control the quantity of heat and the type of flame. They are made in various and types. This torch has certain advantages over the low pressure type.4 kPa). The welding tips (fig. It can be more readily adjusted. some having a one-piece tip either with a single orifice or a of orifices. WELDING TIPS AND MIXERS a. The pressure ranges from 1 to 15 psi (6.
5-10.

b. 5-10 and 5-11) are frequently provided in tip tier assemblies which assure the correct flow of mixed gases for each size tip. Hose identification and composition. the smaller the number. (4) The hose is not impaired by prolonged exposure to light. (2) They are strong. CAUTION Hose should never be used for one gas if it was previously used for another. The hoses used to make the connection between are made especially for this purpose. d. light. One ply is used in the 1/8-to 3/16-in.
.arranged according to the individual manufacturer’s system. the smaller the tip orifice. the oxygen hose is green and the acetylene hose is red. and all threaded fittings for the oxygen hook up are right hand. For heavy duty welding and cutting operations. c. and flexible to permit easy manipulation of the torch. The latter type prevents the hose from kinking or becoming tangled during the welding operation. nonporous. (1) In North America. In Europe. (1) Hoses are built to withstand high internal the regulators and the torch pressures. (3) The rubber used in the manufacture of hose is chemically treated to remove free sulfur to avoid possible spontaneous combustion. Generally. 5-11. internal diameter hose. requiring 1/4-to 1/2-in. The universal type mixer is a separate unit which can be used with tips of various sizes. Hoses are provided with connections at each end so that they may be connected to their respective regulator outlet and torch inlet connections. b. HOSE a. the mixer is assembled with the tip for which it has been drilled and then screwed onto the torch head. Notches are also placed on acetylene fittings to prevent a mixup. three to five plies of braided or wrapped reinforcements are used. all threaded fittings used for the acetylene hook up are left hand. In this tip mixer assembly. Black is sometimes also used for oxygen. blue is used for oxygen and orange for acetylene. hose for light torches. Welding and cutting hoses are obtainable as a single hose for each gas or with the hoses bonded together along their length under a common outer rubber jacket. To prevent a dangerous interchange of acetylene and oxygen hoses. Mixers (fig. (2) The hose is a rubber tube with braided or wrapped cotton or rayon reinforcements and a rubber covering.

(2) Remove the valve protecting caps. (1) Place the oxygen and the acetylene cylinders on a level floor (if they are not mounted on a truck). Pressure Regulators. and bad fittings. b. a. Screw the connecting nuts tightly to insure leakproof seating. (2) Connect the acetylene regulator to the acetylene regulator and the oxygen regulator to the oxygen cylinder. and tie them firmly to a work bench. nicks. The setting up procedures given in a through d below will assure safety to the operator and the apparatus. (4) Connect the red hose to the acetylene regulator and the green hose to the oxygen regulator. acetylene. (3) "Crack" both cylinder valves by opening first the acetylene and then the oxygen valve slightly for an instant to blow out any dirt or foreign matter that may have accumulated during shipment or storage. WARNING
. or other compressed gases when opening them. or other secure anchorage to prevent their being knocked or pulled over. (3) Check hose for burns. WARNING Do not stand facing cylinder valve outlets of oxygen. Note that the acetylene hose connection has left hand threads. Also check threads of cylinders and regulators for imperfections.5-12. When setting up welding and cutting equipment. post. Use either a regulator wrench or a close fitting wrench and tighten the connecting nuts sufficiently to prevent leakage. it is important that all operations be performed systematically in order to avoid mistakes and possible trouble. Cylinders. wall. SETTING UP THE EQUIPMENT WARNING Always have suitable fire extinguishing equipment at hand when doing any welding. (1) Check the regulator fittings for dirt and obstructions. (4) Close the valves and wipe the connection seats with a clean cloth.

Connect the red acetylene hose to the torch needle valve which is stamped "AC or flashback suppressor". Use a soap and water solution to test for leaks at all connections. Release the regulator screws after testing and drain both hose lines by opening the torch needle valves. Blow out the oxygen hose by turning the regulator screw in and then release the regulator screw. Flashback suppressors must be attached to the torch whenever possible. Tighten or replace connections where leaks are found. Read the high pressure gages to check the cylinder gas pressure. Torch. d. Then adjust the acetylene regulator to the required pressure for the tip size to be used (tables 5-1 and 5-2). Connect the green oxygen hose to the torch needle valve which is stamped "OX or flashback suppressor". Test all hose connections for leaks at the regulators and torch valves by turning both regulators’ screws in with the torch needle valves closed. Failure to do this can cause serious injury to personnel and damage to the equipment. Adjustment of Working Pressure.If it is necessary to blow out the acetylene hose. Open the cylinder valves slowly.
. Adjust the acetylene working pressure by opening the acetylene needle valve on the torch and turning the regulator screw to the right. Tighten by hand and adjust the tip to the proper angle. Secure this adjustment by tightening with the tip nut wrench. and press the tip into the mixing head. (5) Release the regulator screws to avoid damage to the regulators and gages. flame. do it in a well ventilated place which is free of sparks. or other sources of ignition. Close the needle valve. Slip the tip nut over the tip. WARNING Purge both acetylene and oxygen lines (hoses) prior to igniting torch. c. Adjust the oxygen working pressure in the same manner.

both high and low pressure gauges on the acetylene and oxygen regulators will register zero. (3) When the above operations are performed properly. then the oxygen valve on the torch. SHUTTING DOWN WELDING APPARATUS a. then close the valve. close the valve. This defect. Leakage of gas between the regulator seat and the nozzle is the principal problem encounter with regulators. 5-14. When gas stops flowing and the gauges read zero. b. Drain the regulators and hoses by the following procedures: (1) Open the torch acetylene valve until the gas stops flowing and the gauges read zero. Then close the acetylene and oxygen cylinder valves. WARNING
. called "creeping regulator". Release the tension on both regulator screws by turning the screws to the left until they rotate freely. (2) Open the torch oxygen valve to drain the oxygen regulator and hose. Close the acetylene valve first. Coil the hoses without kinking them and suspend them on a suitable holder or hanger. Avoid upsetting the cylinders to which they are attached. It is indicated by a gradual increase in pressure on the working pressure gauge when the adjusting screw is fully released or is in position after adjustment.5-13. Shut off the gases. d. is caused by bad valve seats or by foreign matter lodged between the seat and the nozzle. REGULATOR MALFUNCTIONS AND CORRECTIONS a. c.

e. Improved functioning of welding torches is usually due to one or more of the following causes: leaking valves. 5-15. Leaking Valves. cracked.Regulators with leakage of gas between the regulator seat and the nozzle must be replaced immediately to avoid damage to other parts of the regulator or injury to personnel. can be corrected as outlined below: (1) Remove and replace the seat if it is worn. (2) If the malfunction is caused by fouling with dirt or other foreign matter. Rubber diaphragms can be replaced easily by removing the spring case with a vise or wrench. TORCH MALFUNCTIONS AND CORRECTIONS WARNING Defects in oxyacetylene welding torches which are sources of gas leaks must be corrected immediately. The procedure for removing valve seats and nozzles will vary with the make or design. Corrective measures for these common torch defects are described below. as described above. this leakage is particularity dangerous because acetylene at high pressure in the hose is an explosion hazard.
. Satisfactory repairs cannot be made without special equipment. Broken or buckled gage tubes and distorted or buckled diaphragms are usually caused by backfire at the torch. leaks in the mixing head seat. b. Defective bourdon tubes in the gages are indicated by improper action of the gages or by escaping gas from the gage case. as they may result in flashbacks or backfires. f. Gages with defective bourdon tubes should be removed and replaced with new gages. a. leaks across the regulator seats. c. with resultant injury to the operator and/ or damage to the welding apparatus. scored or out-of-round welding tip orifices. Metal diaphragms are sometimes soldered to the valve case and their replacement is a factory or special repair shop job. General. or by failure to release the regulator adjusting screw fully before opening the cylinder valves. clean the seat and nozzle thoroughly and blow out any dust or dirt in the valve chamber. and damaged inlet connection threads. (1) Bent or worn valve stems should be replaced and damaged seats should be refaced. b. or otherwise damaged. Such repairs should not be attempted by anyone unfamiliar with the work. Buckled or distorted diaphragms cannot be adjusted properly and should be replaced with new ones. d. clogged tubes or tips. With acetylene regulators. The leakage of gas.

valves. if the threads are damaged. resulting in injury to the welding operator and/or damage to the equipment. The cleaning drills should be approximately one drill size smaller than the tip orifice to avoid enlarging the orifice during cleaning. Leaks in the mixing head will cause improper mixing of the oxygen and acetylene causing flashbacks. (3) The tip and mixing head should be cleaned either with a cleaning drill or with soft copper or brass wire. WARNING Damages inlet connection threads may cause fires by ignition of the leaking gas. or the presence of foreign matter that has entered the tubes through the hoses will clog tubes. mixing head. Repair by reaming out and trueing the mixing head seat. Leaks due to damaged inlet connection threads can be detected by opening the cylinder valves and keeping the needle valves closed. Such leaks will cause the regulator pressure to drop. (1) Carbon deposits caused by flashbacks or backfire. These are indicated by popping out of the flame and by emission of sparks from the tips accompanied by a squealing noise.85 kPa). If the tubes or tips are clogged. Leaks in the Mixing Heads. the threads should be recut and the hose connections thoroughly cleaned. the hose connection at the torch inlet will be difficult or impossible to tighten. Tips in this condition cause the flame to be irregular and must be replaced.9 to 206. The flame produced will be distorted. Scored or Out-of-Round Tip Orifices. (2) The torch should be disassembled so that the tip. c.
Section II. Clogged Tubes and Tips. A flashback causes the torch head and handle to suddenly become very hot. To correct this defect. greater working pressures will be needed to produce the flame required. and hose can be cleaned and cleaned out with compressed air at a pressure of 20 to 30 psi (137. CAUTION This work should be done by the manufacturer because special reamers are required for trueing these seats. and then blown out with compressed air. e. Also. d.(2) Loose packing may be corrected by tightening the packing nut or by installing new packing and then tightening the packing nut. Damaged Inlet Connection Threads. f. OXYACETYLENE CUTTING EQUIPMENT
.

depending on the purpose for which the tip is used.0 in. CUTTING TORCH AND OTHER CUTTING EQUIPMENT a. The tip (fig. The cutting torch (fig. there is a tube for high pressure oxygen.
b. The cutting torch is controlled by a trigger or lever operated valve. The number of orifices for oxyacetlylene flames ranges from 2 to 6. 5-12).4 mm) to more than 12. In addition. (304. like the welding torch.8 mm) in thickness. Mixed oxygen and acetylene pass through holes surrounding the center holes for the preheating flames. has a tube for oxygen and one for acetylene. The cutting torch is furnished with interchangeable tips for cutting steel from less than 1/4 in. along with a cutting tip or nozzle.5-16. (6. A cutting attachment fitted to a welding torch in place of the welding tip is shown in figure 514.
. 5-13) is provided with a center hole through which a jet of pure oxygen passes.

Arcs and circles are cut by guiding the machine with a radius rod pivoted about a central point.
. Typical cutting machines in operation are shown in figures 5-15 and 5-16. motor driven cutting machines are used to support and guide the cutting torch. Straight line cutting or beveling is accomplished by guiding the machine along a straight line on steel tracks.c. In order to make uniformly clean cuts on steel plate.

cutting speed. The thickness of the material to be cut generally governs the selection of the tip. Cuts that are improperly made will produce ragged.d. (304. The cutting oxygen pressure.8 mm) thick. gas pressures. parallel sided kerfs. OPERATION OF CUTTING EQUIPMENT
. There is a wide variety of cutting tip styles and sizes available to suit various types of work. Table 5-3 identifies cutting tip numbers. and hand-cutting speeds used for cutting mild steel up to 12 in. and preheating intensity should be controlled to produce narrow.
5-17. irregular edges with adhering slag at the bottom of the plates.

NOTE The oxygen and acetylene gas pressure settings listed are only approximate. the weld is formal. This small portion will heat quickly and cutting will start immediately. b. such as a tungsten rod. A good cut will be clean and narrow. Hold this position until the spot has been raised to a bright red heat. it is called a starting rod. the weld is formed by melting and solidifying the base metal at the joint. Hold the torch so that the cutting oxygen lever or trigger can be operated with one hand. In some instances. an arc is produced between an electrode and the work piece (base metal). When used. one or more of the following devices are required: transformers (of which there are several types). e. pressures should be set to effect the best metal cut. and then slowly open the cutting oxygen valve. and control equipment. Move the torch at a speed which will allow the cut to continue penetrating the work.6 mm) above the end of the line to be cut. round bars. (1. portable generators driven by gasoline or diesel engines are used. and is added to the molten pool from a filler rod. In actual use. creating a molten pool. rectifiers. If public utility power is not available. 5-19. Electrical equipment required for arc welding depends on the source from which the electric power is obtained. c. Attach the required cutting tip to the torch and adjust the oxygen and acetylene pressures in accordance with table 5-3. The inner cones of the preheating flames should be about 1/16 in. If the cut has been started properly. On solidifying. Adjust the preheating flame to neutral. A welding rod can be used to start a cut on heavy sections.a. If the power is obtained from public utility lines. time and gas are saved if a burr is raised with a chisel at the point where the cut is to start. In this case. DIRECT CURRENT ARC WELDING MACHINES
. An alternate method employs a nonconsumable electrode. Keep the flame at a 90 degree angle to work in the direction of travel. Use the other hand to steady and maintain the position of the torch head to the work. The arc is formed by passing a current between the electrode and the workpiece across the gap. a shower of sparks will fall from the opposite side of the work. ARC WELDING EQUIPMENT AND ACCESSORIES
5-18. The current melts the base metal and the electrode (if the electrode is a consumable type). GENERAL In electric welding processes. additional metal is required. or heavy sections. When cutting billets. motor generators.
Section III. d.

are used for light shielded metalarc welding and for gas metal-arc welding. (2) The machines rated 200. However. the generator is of the variable voltage type. 300. and is arranged so that the voltage is automatically adjusted to the demands of the arc. The simple equation HP = 1. 30 volts. 40 volts. HP is the engine horsepower and P is the generator rating in watts. 3 phase. The generators are made in six standardized ratings for general purposes as described below:
(1) The machines rated 150 and 200 amperes. and 400 amperes. 5-17). are used for submerged arc welding and for carbon-arc welding. b. a 20 horsepower engine would be used to drive a welding generator with a rated 12 kilowatt output. the voltage may be set manually with a rheostat. The gasoline and diesel engines should have a rated horsepower in excess of the rated output of the generator. This will allow for the rated overload capacity of the generator and for the power required to operate the accessories of the engine. 40 volts. The direct current welding machine has a heavy duty direct current generator (fig.25P/746 can be used. The electric motors must commonly used to drive the welding generators are 220/440 volts.
. For example.a. In most direct current welding machines. They are also used for general purpose job shop work. 60 cycle. (3) Machines rated 600 amperes. c. used for general welding purposes by machine or manual application.

d. A maintenance schedule should be set up to keep the welding machine in good operating condition. and a rectifier to change the alternating current to direct current. Remove all the old grease and replace it with new grease. or selenium dry plates. These machines usually consist of a transform to reduce the power line voltage to the required 220/440 volts. Clean and true the commutator with sandpaper or a commutator stone if it is burned or roughened. In either case. When both voltage and amperage of the welding machine are adjustable. Direct current rectifier type welding machines have been designed with copper oxide. Brushes should be inspected frequently to see if they are making proper contact on the commutator. compressed air. At least once each year. the contacts of the motor starter switches and the rheostat should be cleaned and replaced if necessary. g. The machine should be thoroughly inspected every 3 months and blown free of dust with clean. Welding machines are also manufactured in which current controls are maintained by movement of the brush assembly. a reactor for adjustment of the current. A direct current welding machine is described in TM 5-3431-221-15.
f. Check the bearings twice a year. the desired amperage is obtained by tapping into the generator field coils. ALTERNATING CURRENT ARC WELDING MACHINES
. and is illustrated in figure 5-18. e. 60 cycle input current. 3 phase. the machine is known as dual control type. and is set by means of a selector switch or series of plug receptacles. Sometimes another reactor is used to reduce ripple in the output current. 5-20. dry. silicon. The welding current amperage is also manually adjustable. and that they move freely in the brush holders.

Filler rod is often required to fill the joint. weld puddle. garage and job shop welding. makes continuous adjustment of the output current. In tungsten inert gas (TIG) welding. internal reactions of the transformer are adjustable. The heat of the arc causes the edges of the work to melt and flow together. A steady stream of argon passes through the torch. usually installed on the front or the top of the machine. possible. and that input current is as specified on the nameplate or in the manufacturer’s instruction book. In other types. (also known as GTAW). Most of the alternating current arc welding machines in use are of the single operator. For manual operation in industrial applications. and plug and jack connections should be inspected every 3 months and cleaned or replaced as required. The screws and bearings on machines with screw type adjustments should be lubricated every 3 months. GAS TUNGSTEN-ARC WELDING (GTAW) EQUIPMENT (TIG) a.
. General. Current control is provided in several ways. machines having 200. c. Contacts. which pushes the air away from the welding area and prevents oxidation of the electrode. During the welding operation. and 400 amphere ratings are the sizes in general use. 5-21. One such method is by means of an adjustable reactor in the output circuit of the transformer. switches. The primary input current at no load should be measured and checked once a year to ensure the power factor connecting capacitors are working. The same lubrication schedule applies to chain drives. and heat affected zone. the weld area is shielded from the atmosphere by a blanket of inert argon gas. static transformer type (fig.
b. relays. The transformers are generally equipped with arc stabilizing capacitors. an arc is struck between a virtually nonconsumable tungsten electrode and the workpiece. 5-19). 300. without steps. A handwheel. Machines with 150 ampere ratings are sometimes used in light industrial.a.

(2) Argon is supplied in steel cylinders containing approximately 330 cu ft at a pressure to 2000 psi (13. personal protective equipment should be worn to protect the operator from the arc rays during welding operations. may be used.
. Also. Equipment. A specially designed regulator containing a flowmeter.b. Watercooled torches and air-cooled torches are both available. Each type carries different amperage ratings. The flowmeter provides better adjustment via flow control than the single or two stage regulator and is calibrated in cubic feet per hour (cfh). Equipment consists of the welding torch plus additional apparatus to supply electrical power.790 kPa). and a water inlet and outlet. (1) The basic equipment requirements for manual TIG welding are shown in figure 5-20. Consult the appropriate manual covering the type torch used. A single or two stage regulator may be used to control the gas flow. The correct flow of argon to the torch is set by turning the adjusting screw on the regulator. shielding gas. as shown in figure 5-21. The rate of flow depends on the kind and thickness of the metal to be welded.
NOTE Different types of TIG welding equipment are available through normal supply channels.

it pushes the lighter air molecules aside. and the heat affected zone adjacent to the weld bead.(3) Blanketing of the weld area is provided by a steady flow of argon gas through the welding torch (fig. Since argon is slightly more than 1-1/3 times as heavy as air. the molten weld puddle. effectively preventing oxidation of the welding electrode.
. 5-22).

and the one for heavy duty welding is a copper water-cooled nozzle. It is advisable to use a suitable water strainer or filter at the water supply source. Some TIG welding torches require less than 55 psi (379 kPa) water pressure and will require a water regulator of some type. GAS METAL-ARC WELDING (GMAW) EQUIPMENT a. antifreeze is required if the unit is to be used outdoors during the winter months or freezing weather. Allows the gas to escape. (3) Gas orifice nut. it squeezes against the electrode and leeks it in place. this variation in operation is capable of welding thinner sections than are practical with the conventional spray transfer. (5) Hoses. Check the operating manual for this information. The power source provides two current levels. Three plastic hoses. while a blanket of inert argon gas shields the weld zone from atmospheric contamination. General. Prevents the escape of gas from the top of the torch and locks the electrode in place. 5-22). Pulsed spray welding is a variation of the MIG welding process that is capable of all–position welding at higher energy levels than short circuiting arc welding. otherwise. If a self-contained unit is used. Nomenclature of Torch (fig. the one for light duty welding is made of a ceramic material. gas. GMAW is most commonly referred to as "MIG" welding. (1) Cap. which is superimposed upon the background current at a regulated interval. Two types of nozzles are used. there are several variations of significance. and the electrode power cable. 5-22). MIG welding is a process in which a consumable. carry water. the electrode fits inside and when the cap is tightened. c. and usually one drop is transferred during each pulse. and a "pulsed peak" current.(4) The tremendous heat of the arc and the high current often used usually necessitate water cooling of the torch and power cable (fig. (1) Pulsed spray welding. The combination of the two levels of current produces a steady arc with axial spray transfer at effective welding currents below those required for conventional spray arc welding. 5-22. (2) Collet. The pulse peak is well above the transition current. (4) Gas nozzle. which is too low to produce spray transfer. restricted or blocked passages may cause excessive overheating and damage to the equipment. The cooling water must be clean. and the following text will use "MIG" or "MIG welding" when referring to GMAW. Made of copper. Because the heat input is lower. a steady "background" level. In addition to the three basic types of metal transfer which characterize the GMAW process. such as the one used in the field (surge tank) where the cooling water is recirculated through a pump. connected inside the torch handle.
. Directs the flew of shielding gas onto the weld puddle. bare wire electrode is fed into a weld at a controlled rate of speed.

this combination provides both vertical and horizontal movement. Welding head.5 kg) of wire electrode mounted in the rear of the torch. This method is capable of welding metal sections of from 1/2 in. A variation of continuous gas metal arc welding. and aluminum are commonly joined by this method. Manuals for each type must be consulted prior to welding operations. b. The welding gun remains stationary while a spot weld is being made. Gas metal arc spot welding is a method of joining similar to resistance spot welding and riveting. 5-24). 5-23).08 an) in thickness in a single pass. Water-coded copper shoes span the gap between the pieces being welded to form a cavity for the molten metal. MIG Equipment. The eletrogas variation essentially combines the mechanical features of electroslag welding (ESW) with the MIG welding process.
. and T-joints in the vertical position. and electrode spools are mounted on the carriage. (3) Electrogas welding. using a spool-on-gun torch. Deposition rates of 35 to 46 lb (16 to 21 kg) per hour per electrode can be achieved. The torch handle contains a complete motor and gear reduction unit that pulls the welding wire electrode from a 4 in. A carriage is mounted on a vertical column. and a welding contractor (fig. the process fuses two pieces of sheet metal together by penetrating entirely through one piece into the other. The unit consists of a torch (fig. a voltage control box. (5. The electrogas (EG) variation of the MIG welding process is a fully automatic. (1) The MIG welding unit is designed for manual welding with small diameter wire electrodes. (102 mm) diameter spool containing 1 lb (0. corner. controls. NOTE Different types of MIG welding equipment are available through normal supply channels. Both the carriage and the copper shoes move vertically upwards as welding progresses. high deposition rate method for the welding of butt. stainless steel.(2) Arc spot welding. (13 mm) to more than 2 in. No joint preparation is required other than cleaning of the overlap areas. Mild steel. The welding head may also be oscillated to provide uniform distribution of heat and filler metal.

.

With the trigger depressed.51 mm) larger than the size of the wire electrode being used. As long as the wire electrode advances through the tube. Many types of metal may be welded provided the welding wire electrode is of the same composition as the base metal. the actual welding operation starts and the motor pulls the electrode from the spool at the required rate of feed. An insulated lock screw is provided which secures the contact tube in the torch. under spring tension. A thumbscrew applies tension as required. 5-23). This assembly is made of plastic which prevents arc spatter from jamming the wire electrode on the spool. constant-current welding power supply. The nozzle is made of copper to dissipate heat and is chrome-plated to reflect the heat. Nomenclature of Torch. This is a smooth roller. c. the current for running the motor comes from the 110 V ac-dc source. The bushings are made of nylon for long wear. (3) The unit is designed for use with an ac-dc conventional.(2) Three basic sizes of wire electrode maybe used: 3/32 in. NOTE If for any reason the wire electrode stops feeding.25 to 0.02 in. When the trigger is depressed. (6) Spool enclosure assembly (fig. 3/64 in. the welding contactor is closed. an arc will be drawn at
. Gasoline engine-driven arc welding machines issued to field units may be used as both a power source and a welding source. (2.19 mm). 5-23). 5-23). (2) Nozzle and holder (fig. (0.59 mm). which pushes the wire electrode against the feed roll and allows the wire to be pulled from the spool. The current for this rotor is supplied by the welding generator. (4) Pressure roll assembly (fig. and 1/16 in. (1.01 to 0. (5) Motor (fig. 5-23). The holder is made of stainless steel and is connected to an insulating material which prevents an arc from being drawn between the nozzle and the ground in case the gun canes in contact with the work. They must be changed to suit the wire electrode size when the electrode wire is changed. (3) Inlet and outlet guide bushings (fig. A small window allows the operator to visually check the amount of wire electrode remaining on the spool. This tube is made of copper and has a hole in the center of the tube that is from 0.38 mm). When the inch button is depressed. 5-23). 5-23). (1) Contact tube (fig. and the rotor pulls the wire electrode from the spool before starting the welding operation. The contact tube transfers power from the electrode cable to the welding wire electrode. thereby allowing the welding current to flow through the contact tube. The contact tube and the inlet and outlet guide bushings must be charged when the size of the wire electrode is changed. a burn-back will result. (1.

(10) Voltage pickup cable (fig. allowing a flow of argon gas to pass out of the nozzle to shield the weld zone. This cable must be attached to the ground cable at the workpiece. (8) Argon gas hose (fig. (7) Welding contactor (fig. This hose is connected from the voltage control box to the argon gas regulator on the argon cylinder. a protective shield must be installed to prevent the argon gas from being blown away from the weld zone and allowing the weld to become contaminate.
. Should the wire electrode stop feeding while the trigger is still being depressed. causing it to melt off.the end of the wire electrode. (11) Torch switch and grounding cables (fig. The positive cable from the dc welding generator is connected to a cable coming out of the welding contactor. (1) Press the inch button and allow enough wire electrode to emerge from the nozzle until 1/2 in. (4) When the contactor closes. Starting to Weld. (3) Press the torch trigger. The electrode cable enters through the welding current relay and connects into the argon supply line. closing the contactor. (9) Electrode cable (fig. and the ground cable is connected to the workpiece. 5-24). This is called burn-back. and the torch grounding cable is connected to the case of the voltage control box. With the main line switch "ON" and the argon gas and power sources adjusted properly. 5-24). 5-24). 5-23. (2) When welding in the open air. Both then go out of the voltage control box and into the torch in one line. The torch switch cable is connected into the voltage control box. This supplies the current to the motor during welding when the trigger is depressed. the argon gas solenoid valve opens. (5) At the same time the contactor closes. 5-24). The electrode cable and the welding contactor cable are connected between the welding contactor and voltage control box as shown. OPERATING THE MIG a. This sends current down the torch switch cable and through the contactor cable. the welding circuit from the generator to the welding torch is completed. the arc will then form at the end of the contact tube. (13 mm) protrudes beyond the end of the nozzle. 5-24). the operator may begin to weld.

(4) Close the pressure roller and secure it in place. turn the dial counterclockwise. CAUTION To prevent overloading the torch motor when stopping the arc. (2) Unroll the straighten 6 in. thereby decreasing the speed of wire electrode being fed from the spool. release the trigger. b. protects and controls the torch motor. brake. (152 mm) of wire electrode from the top of the spool. Press the inch button. (1) Two 10-ampere fuses. and pressure roll assembly (fig. Turning the dial clockwise will increase the amount of resistance. (13 mm) protruding beyond the end of the nozzle. between 50 and volts dc is generated. located on the front of the voltage control box. c. Setting the Wire Electrode Feed. Installing the Wire Electrode. 523). (3) Feed this straightened end of the wire electrode into the inlet and outlet bushings. never snap the arc out by raising the torch without first releasing the trigger. (1) Open the spool enclosure cover assembly. The gun is held at a 90 degree angle to the work but pointed at a 10 degree angle toward the line of travel. (1) A dial on the front of the voltage control box. (2) A 1-ampere fuse. is used to regulate the speed of the wire electrode feed. d. (2) To increase the speed of the wire electrode being fed from the spool.(6) Lower the welding helmet and touch the end of the wire electrode to the workpiece. This voltage is picked up by the voltage pickup cable shunted back through the voltage control box into a resistor. This decreases the amount of resistance across the arc and allows the motor to turn faster. then place spool onto the mounting shaft. There it is reduced to the correct voltage (24 V dc) and sent to the torch motor.
. Fuses. feeding the wire electrode until there is 1/2 in. located at the front of the voltage control box. (7) Welding will continue as long as the arc is maintained and the trigger is depressed. labeled WELDING CONTROL. (3) At the instant that the wire electrode touches the work. protect and control the electrical circuit within the voltage control box.

(9.
. they are 5-3/8 in. the argon gas continues to flow. Reassemble the contact ring and nameplate. (137 mm) long.2 mm) contact tube. making certain that the pins protruding from the shaft engage the slots in the feed roll. a maximum of 3/8 in. then drill out the contact tube. use a No. remove the nameplate on top of the torch. One end of the flexible cable is attached to the electrode holder and the other end to the negative side of a direct current welding machine for straight polarity. When burn-backs occur. File a flat spot on top of the guide tube. 46 or 47 drill bit. Place a new feed roll on the feed roll mounting shaft.e. and stops flowing when the torch trigger is released. withdrawing the wire electrode and causing a severe burn-back. (1. f. (1) Flip the argon switch on the front of the voltage control panel to the MANUAL position. (4) When in the MANUAL position. (2) To replace the feed roll. The generator is set on reverse polarity. flip the argon switch to the AUTOMATIC POSITION. Cables. Preventive Maintenance. When the contact tubes are new. 5-24. Welding in the vertical or overhead positions will cause spatter to fall down inside the torch nozzle holder and restrict the passage of the argon gas. (2) Turn on the argon gas cylinder valve and set the pressure on the regulator. For a 3/64 in. tough. resilient rubber jackets are required. the flathead screw and retainer from the feed roll mounting shaft. the other end to the work table or other suitable ground. the argon gas flows only when the torch trigger is depressed. Two welding cables of sufficient current carrying capacity with heavy. When in the AUTOMATIC position. One of the cables should be composed of fine copper strands to permit as much flexibility as the size of the cable will allow. For those machines not equipped with polarity switches. One end of the less flexible cable is attached to the ground lug or positive side of the direct current welding machine. and the contact ring and feed roll. Reclaiming Burned-Back Contact Tubes. (1) Keep all weld spatter cleaned out of the inside of the torch. Generator Polarity. Most machines are equipped with a polarity switch which is used to change the polarity without interchanging the welding cables at the terminals of the machine. OTHER WELDING EQUIPMENT a. h. Keep all hose connections tight. When set on straight polarity. (3) When the proper pressure is set on the regulator. the cables are reversed at the machine. the torch motor will run in reverse. Setting the Argon Gas Pressure. place a drill pilot on the contact tube.5 mm) may be filed off. g. for reverse polarity.

One of the two electrode holders is movable. a second equipped with a heat shield. 5-25). The jaws can be opened by means of a lever held in place by a spring (fig. This is an insulated clamp in which a metal electrode can be held at any desired angle. oxides and slag. 5-26). through which both hydrogen gas and electric current flow. The hydrogen is supplied to a tube in the rear of the handle from which it is led into the two current carrying tubes by means of a manifold. c. the third type is watercooled. One type holds two electrodes and is similar in design to the atomic hydrogen torch. A chipping hammer is required to loosen scale. A wire brush is used to clean each weld bead before further welding. Accessories. An electrode holder is an insulated clamping device for holding the electrode during the welding operation. (1) Chipping hammer and wire brush.
.b. (1) Metal-arc electrode holder. Figure 5-27 shows a chipping hammer with an attachable wire brush. and the gap between this and the other holder is adjusted by means of a trigger on the handle (fig. This electrode holder or torch consists of two tubes in an insulated handle. This holder is manufactured in three specific types. as explained below. The design of the holder depends on the welding process for which it is used.
(3) Carbon-arc electrode holder.
(2) Atomic hydrogen torch. but has no gas tubes. Electrode Holders.

A mixture of water. strips. and fire clay or carbon powder can be used for making molds. or bars of copper or cast iron should be available for use as backup bars in welding light sheet aluminum and in making certain types of joints. A welding table should be of all-steel construction. A typical design for a welding table is shown in figure 5-28. glass.
(3) Clamps and backup bars.(2) Welding table. A container for electrodes with an insulated hook to hold the electrode holder when not in use should be provided. Blocks. Workpieces for welding should be clamped in position with C-clamps or other clamp brackets.
. Carbon blocks. or other fire-resistant material should also be available. fire clay. These materials are used to form molds which hold molten metal within given limits when building up sections.

stabilizes the arc. Types of Electrodes. 1 is for all positions. alternating or direct current. and the type of current and polarity required. it absorbs oxygen and nitrogen. When molten metal is exposed to air. 5-25. straight or reverse polarity. The type used depends on the specific properties required in the weld deposited. 3 is for flat position only. which protects the metal from damage. 2 is for flat and horizontal positions only. and becomes brittle or is otherwise adversely affected. high tensile strength. 0 indicates the classification is not used. General. (2) The first two (or three) digits indicate tensile strength (the resistance of the material to forces trying to pull it apart) in thousands of pounds per square inch of the deposited metal. Classification of Electrodes. Goggles. ductility. the type of base metal to be welded. The electrode identification system for steel arc welding is set up as follows: (1) E indicates electrode for arc welding. flat. ELECTRODES AND THEIR USE a.. The metal-arc electrodes may be grouped and classified as bare electrodes. or overhead). and shielding arc or heavy coated electrodes. and improves the weld in the ways described below. b. (4) The fourth (or fifth) digit indicates the type of electrode coating and the type of power supply used.d. (3) The third (or fourth) digit indicates the position of the weld. and polarity position designated by the fourth (or fifth) identifying digit of the electrode classification are as listed in table 5-4. c.
. These include corrosion resistance. e. A slag cover is needed to protect molten or solidifying weld metal from the atmosphere. This cover can be obtained from the electrode coating. Goggles with green lenses shaped to cover the eye orbit should be available to provide glare protection for personnel in and around the vicinity of welding and cutting operations (other than the welder). horizontal. The American Welding Society’s classification number series has been adopted by the welding industry. the position of the weld (i. vertical. NOTE These goggles should not be used in actual welding operations. (5) The types of coating. light coated electrodes. welding current.

used in all positions. These wire drawing coatings have some slight stabilizing effect on the arc but are otherwise of no consequence. is used in all positions.
. Bare Electrodes. with alternating or reverse polarity direct current. (b) The first three digits indicated the American Iron and Steel type of stainless steel. Bare electrodes are made of wire compositions required for specific applications.(6) The number E6010 indicates an arc welding electrode with a minimum stress relieved tensile strength of 60. These electrodes have no coatings other than those required in wire drawing. and reverse polarity direct current is required. d. (c) The last two digits indicate the current and position used.000 psi. A diagram of the transfer of metal across the arc of a bare electrode is shown in figure 5-29. (3) The electrode identification system for stainless steel arc welding is set up as follows: (a) E indicates electrode for arc welding. Bare electrodes are used for welding manganese steel and other purposes where a coated electrode is not required or is undesirable. (d) The number E-308-16 by this system indicates stainless steel Institute type 308.

.e. Light Coated Electrodes. spraying. and other inorganic substances or combinations thereof. sulfur. but it is quite thin and does not act in the same manner as the shielded arc electrode type slag. They are listed under the E45 series in the electrode identification system. Shielded arc or heavy coated electrodes have a definite composition on which a coating has been applied by dipping or extrusion. A light coating has been applied on the surface by washing. The mineral coatings consist of sodium silicate. sodium. and in some cases added minerals.
f. Shielded Arc or Heavy Coated Electrodes. metallic oxides. and those with coatings of combinations of mineral and cellulose. or titanium. The arc action obtained with the shielded arc or heavy coated electrode is shown in figure 5-31. tumbling. e. Cellulose coated electrodes protect the molten metal with a gaseous zone around the arc as well as slag deposit over the weld zone. (1) Light coated electrodes have a definite composition. those with mineral coatings. and hard surfacing. (3) Some of the light coatings may produce a slag. (b) It changes the surface tension of the molten metal so that the globules of metal leaving the end of the electrode are smaller and more frequent. The arc action obtained with light coated electrodes is shown in figure 5-30. changed into small particles with an electric charge) into the arc stream. (2) The coating generally serves the following functions: (a) It dissolves or reduces impurities such as oxides. (c) It increases the arc stability by introducing materials readily ionized (i.
. or wiping to improve the stability and characteristics of the arc stream. and phosphorus. clay. The mineral coated electrode forms a slag deposit only. cast iron. The cellulose coatings are composed of soluble cotton or other forms of cellulose with small amounts of potassium. dipping. The electrodes are manufactured in three general types: those with cellulose coatings. The shielded arc or heavy coated electrodes are used for welding steels. brushing. making the flow of molten metal more uniform.

. (2) The electrodes reduce impurities such as oxides. low strength and poor resistance to corrosion. sulfur. Since the slag solidifies at a relatively slow rate. (5) The coatings contain silicates which will form a slag over the molten weld and base metal. it holds the heat and allows the underlying metal to cool and slowly solidify.g. the vaporized and melted coating causes the molten metal at the end of the electrode to break up into fine. (1) These electrodes produce a reducing gas shield around the arc which prevents atmospheric oxygen or nitrogen from contaminating the weld metal. The nitrogen would cause brittleness. and in some cases. This slow solidification of the metal eliminates the entrapment of gases within the weld and permits solid impurities to float to the surface. removing alloying elements and causing porosity. (6) The physical characteristics of the weld deposit are modified by incorporating alloying materials in the electrode coating. The fluxing action of the slag will also produce weld metal of better quality and permit welding at higher speeds. (4) By reducing the attractive force between the molten metal and the end of the electrode. small particles. and phosphorus so that these impurities will not impair the weld deposit. Functions of Shielded Arc or Heavy Coated Electrodes. or by reducing the surface tension of the molten metal. (3) They provide substances to the arc which increase its stability and eliminate wide fluctuations in the voltage so that the arc can be maintained without excessive spattering. low ductility. The oxygen would readily combine with the molten metal. Slow cooling also has an annealing effect on the weld deposit.

Electrodes exposed to damp air for more than two or three hours should be dried by heating in a suitable oven (fig.3 to 0. (d) Brown -.5 percent zirconium. reduces heat losses and increases the temperature at the end of the electrode. 5 percent tungsten) electrodes are generally used on less critical welding operations than the tungstens which are alloyed. (b) Yellow -. or sheath (fig. (a) Green -. Electrodes must be kept dry. (2) Tungsten electrodes can be identified as to type by painted end marks as follows.
i. Tungsten Electrodes. Moisture destroys the desirable characteristics of the coating and may cause excessive spattering and lead to the formation of cracks in the welded area.0. (8) The coating produces a cup. concentrates and directs the arc.1 percent thorium.2 percent thorium.5 percent zirconium. Storing Electrodes.(7) The coating insulates the sides of the electrode so that the arc is concentrated into a confined area. 5-31) at the tip of the electrode which acts as a shield.pure tungsten. they should be stored in a moisture proof container.3 to 0. 5-32) for two hours at 500°F (260°C). h. (c) Red -. This type of electrode has a relatively low current-carrying capacity and a low resistance to contamination. After they have dried. This facilitates welding in a deep U or V groove. Electrodes should not be used if the core wire is exposed. tungsten containing 1 or 2 percent thorium. (1) Nonconsumable electrodes for gas tungsten-arc (TIG) welding are of three types: pure tungsten. Bending the electrode can cause the coating to break loose from the core wire.
. (3) Pure tungsten (99. and tungsten containing 0. cone.

There is. Direct Current Welding. In direct current welding. Maintenance of electrode shape and the reduction of tungsten inclusions in the weld can best be accomplished by superimposing a highfrequency current on the regular welding current. (1) For dcsp. the welding machine connections are electrode positive and workpiece negative. (6. and greater resistance to contamination. (5) Tungsten electrodes containing 0. the welding current circuit may be hooked up as either straight polarity (dcsp) or reverse polarity (dcrp). some indication of better performance in certain types of welding using ac power. however.3 to 0. The tungsten electrode of torch should be inclined slightly and the filler metal added carefully to avoid contact with the tungsten. This will prevent contamination of the electrode.2 mm) might be used for butt joints in light gage material. When electrodes are not grounded. For dcrp. better arc-starting and arc stability. while an extension of approximately 1/4 to 1/2 in.(4) Thoriated tungsten electrodes (1 or 2 percent thorium) are superior to pure tungsten electrodes because of their higher electron output. longer life. The polarity recommended for use with a specific type of electrode is established by the manufacturer. electron flow is from electrode to workpiece. Tungsten electrodes alloyed with thorium and zirconium retain their shape longer when touch-starting is used.5 percent zirconium generally fall between pure tungsten electrodes and thoriated tungsten electrodes in terms of performance. and replaced in the torch. high current-carrying capacity. If contamination does occur. reground. an extension beyond the gas cup of 1/8 in. the electrode must be removed.
. (3. For example.4 to 12. 5-33). electron flow is from workpiece to electrode.
(7) The electrode extension beyond the gas cup is determined by the type of joint being welded. 5-34). Tungsten electrode points are difficult to maintain if standard direct current equipment is used as a power source and touch-starting of the arc is standard practice. the welding machine connections are electrode negative and workpiece positive (fig. j. (6) Finer arc control can be obtained if the tungsten alloyed electrode is ground to a point (fig. they must be operated at maximum current density to obtain reasonable arc stability.7 mm) might be necessary on some fillet welds.

because of the larger electrode diameter and lower currents generally employed. this amount of current would melt off the electrode and contaminate the weld metal. a 1/16-in. This will produce greater heat on the negative side of the arc. DCRP welding. relatively shallow weld (fig. However.(2) For both current polarities.
. when heavy coated electrodes are used. dcrp requires a larger diameter electrode than does dcsp. (3) The different heating effects influence not only the welding action.6-mm) diameter pure tungsten electrode can handle 125 amperes of welding current under straight polarity conditions. while another type of coating on the same electrode may provide a more desirable heat balance with reverse polarity. deep weld. Hence. but also the shape of the weld obtained. DCSP welding will produce a wide. however. Thus. If the polarity were reversed.4-mm) diameter pure tungsten electrode is required to handle 125 amperes dcrp satisfactorily and safely. for any given welding current. One type of coating may provide the most desirable heat balance with straight polarity. 535). a 1/4-in. gives a narrow. the greatest part of the heating effect occurs at the positive side of the arc. the composition of the coating and the gases it produces may alter the heat conditions. (1. (6. The workpiece is dcsp and the electrode is dcrp. For example.

bare. k. This surface cleaning action is caused either by the electrons leaving the plate or by the impact of the gas ions striking the plate. half of each complete alternating current (ac) cycle is dcsp. (1) Alternating current welding. which tends to break up the surface oxides. The wrong polarity will cause the arc to emit a hissing sound. straight polarity is used with all mild steel. and dirt usually present. (6) The proper polarity for a given electrode can be recognized by the sharp. monel. and nickel. or light coated electrodes. theoretically. and the welding bead will be difficult to control. cracking sound of the arc. the other half is dcrp. bronze. As shown in figure 5-36. Reverse polarity is also used with sane types of electrodes for making vertical and overhead welds.(4) One other effect of dcrp welding is the so-called plate cleaning effect.
. (5) In general. This can be best explained by showing the three current waves visually. Reverse polarity is used in the welding of non-ferrous metals such as aluminum. Alternating Current Welding. is a combination of dcsp and dcrp welding.

the current wave would be similar to figure 5-37. (c) A longer arc is possible.
. scale. to prevent the flow of current in the reverse polarity direction. high-frequency current on the welding current gives the following advantages: (a) The arc may be started without touching the electrode to the workpiece. Direct Current Arc Welding Electrodes. together with both dcsp and dcrp welds for comparison.
l. (e) The use of wider current range for a specific diameter electrode is possible.(2) Moisture. in no current at all flowed in the reverse polarity direction. Superimposing this high-voltage. high-frequency. This high-frequency current jumps the gap between the electrode and the workpiece and pierces the oxide film. This is called rectification.
(3) To prevent rectification from occurring. (d) Welding electrodes have longer life. This is particularly useful in surfacing and hardfacing operations. low-power current. (b) Better arc stability is obtained. oxides. etc. it is common practice to introduce into the welding current an additional high-voltage. For example. partially or completely. on the surface of the plate tend. thereby forming a path for the welding current to follow.. (4) A typical weld contour produced with high-frequency stabilized ac is shown in figure 5-38.

manganese oxide. silicon. and stabilize the arc. the composition and uniformity of the wire is an important factor in the control of arc stability. In bare electrodes. Sulfur acts as a slag. and "cold shortness" (i. Alternating current is more desirable while welding in restricted areas or when using the high currents required for thick sections because it reduces arc blow. e. and lack of fusion in the weld. straight polarity electrodes will provide less penetration than reverse polarity electrodes. brittle when below red heat) in the weld. (3) When phosphorus or sulfur are present in the electrode in excess of 0. e. Electrode Defects and Their Effects. These defects increase in magnitude as the carbon content of the steel increases. Arc blow causes blowholes. and iron sulphate unstable. Iron oxide. (2) In most cases. calcium oxide.
.04 percent.. m. (2) Aluminum or aluminum oxide (even when present in 0. Many.(1) The manufacturer’s recommendations should be followed when a specific type of electrode is being used. (2) Alternating current is used in atomic hydrogen welding and in those carbon arc processes that require the use of two carbon electrodes. Sulfur is particularly harmful to bare. In carbon-arc processes where one carbon electrode is used.01 percent). brittle when above red heat). (1) If certain elements or oxides are present in electrode coatings. but not all. bare and alloy steel electrodes. low-carbon steel electrodes with a low manganese content. Recommendations from the manufacturer also include the type of base metal for which given electrodes are suited. Alternating Current Arc Welding Electrodes. and for this reason will permit greater welding speed. the arc stability will be affected. Phosphorus causes grain growth. Thin or heavy coatings on the electrodes will riot completely remove the effects of defective wire. Good penetration can be obtained from either type with proper welding conditions and arc manipulation. corrections for poor fit-ups. Manganese promotes the formation of sound welds. silicon dioxide. nonferrous. they will impair the weld metal because they are transferred from the electrode to the molten metal with very little loss. because the electrode will be consumed at a lower rate. Direct current is preferred for many types of covered. or both. and other specific conditions. In general. It permits a uniform rate of welding and electrode consumption. slag inclusions. direct current straight polarity is recommended. and causes "hot shortness" (i. n.. direct current shielded arc electrodes are designed either for reverse polarity (electrode positive) or for straight polarity (electrode negative). breaks up the soundness of the weld metal. brittleness. (1) Coated electrodes which can be used with either direct or alternating current are available. of the direct current electrodes can be used with alternating current.

the weld programmer completes the sequence.
. resistance flash welding. Principal Elements of Resistance Welding Machines. and a secondary circuit. In a mechanized setup. (3) The control equipment (timing devices) to initiate the time and duration of the current flow. as well as the sequence and the time of other parts of the welding cycle. the welding operator positions the work between the electrodes and pushes a switch to initiate the weld. and economic considerations. the electrode will produce welds inferior to those produced with an electrode of the same composition that has been properly heat treated. then welded and ejected without welding operator assistance. production schedules.
Section IV. and the time the current flows through the work. in a circuit of which the work is a part. Standard resistance welding machines are capable of welding a variety of alloys and component sizes. This equipment may also control the current magnitude. parts are automatically fed into a machine. Resistance welds are made with either semiautomatic or mechanized machines. c. resistance seam welding. the pressure that the electrodes transfer to the work. with the maximum heat being generated at the surfaces being joined. The amount of current employed and the time period are related to the heat input required to overcome heat losses and raise the temperature of the metal to the welding temperature. (2) A mechanical system consisting of a machine frame and associated mechanisms to hold the work and apply the welding force. With the semiautomatic machine. Resistance welding machines are classified according to their electrical operation into two basic groups: direct energy and stored energy. and by the application of pressure. Heat is generated by the passage of electrical current through a resistance current. Pressure is required throughout the welding cycle to assure a continuous electrical circuit through the work. The three factors involved in making a resistance weld are the amount of current that passes through the work. There are seven major resistance welding processes: resistance projection welding. RESISTANCE WELDING EQUIPMENT
5-26. given the wire core of an electrode. quality requirements. Electrical Operation. A resistance welding machine has three principal elements: (1) An electrical circuit with a welding transformer and a current regulator. b. is not uniform.(4) If the heat treatment. Resistance welding is a group of welding processes in which the joining of metals is produced by the heat obtained from resistance of the work to the electric current. construction materials. RESISTANCE WELDING a. and resistance high frequency welding. including the electrodes which conduct the welding current to the work. General. resistance upset welding. resistance spot welding. resistance percussion welding. The selection of resistance welding equipment is usually determined by the joint design.

press. In these machines. and multiple type. The electrodes must be positioned so that both are in the plane of the
. Spot Welding. d. They are readily adaptable for spot welding of most weldable metals. portable. These machines consist essentially of a cylindrical arm or extension of an arm which transmits the electrode force and in most cases. (1) There are several types of spot welding machines. with its essential operating elements for manual operation. including rocker arm. is shown in figure 5-39. The electrodes are composed of a copper alloy and are assembled in a manner by which considerable force or squeeze may be applied to the metal during the welding process. The travel path of the upper electrode is in an arc about the fulcrum of the upper arm. the electrode jaws are extended in such a manner as to permit a weld to be made at a considerable distance from the edge of the base metal sheet. A typical spot welding machine.
(a) Rocker arm type. the welding current.Machines in both groups may be designed to operate on either single-phase or three-phase power.

(c) Rapid follow up of the electrode force by employing anti-friction bearings and lightweight. a variable or dual force cycle to permit forging the weld nugget. (2) When spot welding aluminum. For most applications. (b) Precise electronic control of current and length of time it is applied. A typical portable welding gun consists of a frame. Because of the radial motion of the upper electrode. holders. or both. (d) High structural rigidity of the welding machine arms. They may be designed for spot welding. The design of the gun is tailored to the needs of the assembly to be welded. and platens in order to minimize deflection under the high electrode forces used for aluminum. the moveable welding head travels in a straight line in guide bearings or ways. They utilize a number of transformers. However. and an initiating switch. solid. hand grips.
. an air or hydraulic actuating cylinder. or manually with small bench units. (b) Press type. these machines are not recommended for projection welding. These features include the following: (a) Ability to handle high current for short welding times. These are special-purpose machines designed to weld a specific assembly. in some cases. Force may be applied by air or hydraulic cylinders. lower electrode. Press type machines are classified according to their use and method of force application. The same basic welding gun is used for the designs. Force is applied directly to the electrode through a holder by an air or hydraulic cylinder. A typical portable spot welding machine consists of four basic units: a portable welding gun or tool. a rectifier.horn axes. or where variations in parts will not permit consistent contact with a large. Equalizing guns are often used where standard electrodes are needed on both sides of the weld to obtain good heat balance. (c) Portable type. a welding transformer and. (d) Multiple spot welding type. low-inertia heads. the best results are obtained only if certain refinements are incorporated into these machines. conventional spot welding machines used to weld sheet metal may be used. the lower electrode is made of a piece of solid copper alloy with one or more electrode alloy inserts that contact the part to be welded. In this type of machine. but it is mounted on a special "C" frame similar to that for a portable spot welding gun. The entire assembly can move as electrode force is applied to the weld location. projection welding. an electrical contactor and sequence timer. and to reduce magnetic deflections. and a cable and hose unit to carry power and cooling water between the transformer and welding gun.

both of these
. Projection Welding. Flash weld-fig is generally preferred for joining components of equal cross section end-to-end. the electrode is stationary and the work is moved. and wheel electrodes. The effectiveness of this type of welding depends on the uniformity of the projections or embossments on the base metal with which the electrodes are in contact (fig. the work is held in a fixed position and a wheel type electrode is passed over it. The projection welding dies or electrodes have flat surfaces with larger contacting areas than spot welding electrodes. 5-40). e. Refrigerated cooling is often helpful. Portable seam welding machines use this principle.
f. rod. electronic controls and contactor. a welding head consisting of an air cylinder. However. Flat nose or special electrodes are used. A seam welding machine is similar in principle to a spot welding machine. (f) Postheat current to allow slower cooling of the weld. except that wheel-shaped electrodes are used rather than the electrode tips used in spot welding. The press type resistance welding machine is normally used for projection welding. a ram. (g) Good cooling of the Class I electrodes to prevent tip pickup or sticking. the secondary circuit connections. Upset and Flash Welding. Flash welding machines are generally of much larger capacity than upset welding machines. if used. Seam welding machine controls must provide an on-off sequencing of weld current and a control of wheel rotation. In some machines. Seam Welding. or bar of small cross section and to join the seam continuously in pipe or tubing. g. the type used depending on the service requirements. The components of a standard seam welding machine include a main frame that houses the welding transformer and tap switch. the lower electrode mounting and drive mechanism. Several types of machines are used for seam welding. In the traveling fixture type seam welding machine. Flash and upset welding machines are similar in construct ion. The major difference is the motion of the movable platen during welding and the mechanisms used to impart the motion. and an upper electrode mounting and drive mechanism. Upset welding is normally used to weld wire.(e) Slope control to permit a gradual buildup and tapering off of the welding current.

into which a magnesite stone thimble is fitted. movable platen. a tap switch. A wax pattern is then made around the joint in the size and shape of the intended weld. The mold should be properly vented to permit the escape of gases and to allow the proper distribution of the thermit metal at the joint. The metals that are to be joined serve as electrodes. Molten steel is produced by the thermit reaction in a magnesite-lined crucible. General. Two types of welding machines are used in percussion welding: magnetic and capacitor discharge. stationary platen. In preparing the joint for thermit welding. This thimble provides a passage through which the molten steel is discharged into the mold. The crucible is charged by placing the correct quantity of thoroughly mixed thermit material in it. Pressure is applied progressively during or immediately following the electrical discharge. The process is entirely automatic and utilizes equipment designed specifically for this process. alined. clamping mechanisms and fixtures. Electrodes that hold the parts and conduct the welding current to them are mounted on the platens. and a flashing and upsetting mechanism.
Section V. electrical controls.
. A thermit welding crucible and mold is shown in figure 5-41. Percussion Welding. and the rapid application of an upsetting force after heating is completed. controls. The hole through the thimble is plugged with a tapping pin. The process is similar to flash and upset welding. The sand mold is then heated to melt out the wax and dry the mold. THERMIT WELDING EQUIPMENT
5-27. a transformer. Thermit material is a mechanical mixture of metallic aluminum and processed iron oxide. This process joins metals with the heat generated from the resistance of the work pieces to a high frequency alternating current in the 10. This process uses heat from an arc produced by a rapid discharge of electrical energy to join metals. THERMIT WELDING (TW) a.000 hertz range. A mold made of refractory sand is built around the wax pattern and joint to hold the molten metal after it is poured. (1) A standard flash welding machine consists of a main frame. (2) Upset welding machines consist of a main frame that houses a transform and tap switch.000 to 500. and means to upset the joint. h. electrodes to hold the parts and conduct the welding current. and tooling. and held firmly in place. A unit generally consists of a modified press-type resistance welding machine with specially designed transform.processes can be performed on the same type of machine. a magnesite stone is burned. i. which is covered with a fireresistant washer and refractory sand. the parts to be welded must be cleaned. At the bottom of the crucible. High Frequency Welding. If necessary. metal is removed from the joint to permit a free flow of the thermit metal into the joint. A primary contactor is used to control the welding current.

or it may be equipped
. The two types used in hand forge welding are described below. and ash gate. A portable forge may have a handcrank blower. is the most important component of forge welding equipment. Portable Forge. a tuyere. FORGES Forge welding is a form of hot pressure welding which joins metals by heating them in an air forge or other furnace. base with air inlet. and a blower. The valve handle is also used to free the valve from ashes. FORGE WELDING TOOLS AND EQUIPMENT 5-28. a. as shown in figure 5-42. The essential parts of a forge are a hearth. a water tank. and then applying pressure. The valve can be set in three different positions to regulate the size and direction of the blast according to the fire required. It is made of cast iron and consists of a fire pot. One type of portable forge is shown in figure 5-42. The tuyere is a valve mechanism designed to direct an air blast into the fire. which may be either portable or stationary. The air blast passes through the base and is admitted to the fire through the valve. blast valve. The forge.Section VI.

because the removal of furies and smoke is positive. Stationary Forge. The opening of these slots can be varied to regulate the volume of the blast and the size of the fire. tempered tool steel which is welded to the top of the anvil. the smoke and gases pass up through the hood and chimney by natural draft or are drawn off by an exhaust fan.with an electric blower. The blower produces air blast pressure of about 2 oz per sq in. The table or cutting block is soft so that cutters and chisels caning in contact with it will not be dulled.
. A hood is provided on the forge for carrying away smoke and fumes. The stationary forge is similar to the portable forge except that it is usually larger with larger air and exhaust connections. the positions of which can be controlled by turning the valve. 5-43) is usually made of two forgings or steel castings welded together at the waist. In the updraft type. The downdraft forge permits better air circulation and shop ventilation. (1) The anvil (fig. like portable forges. The air blast valve usually has three slots at the top. 5-29. the smoke and fumes are drawn down under an adjustable hood and carried through a duct by an exhaust fan that is entirely separate from the blower. The stationary forges. The forge may have an individual blower or there may be a large capacity blower for a group of forges. It cannot be easily damaged by hammering.
b. Anvil. FORGING TOOLS a. The face is made of hardened. In the downdraft type. are available in both updraft and downdraft types.

fullers. The hardy hole is square and is designed to hold the hardy.
. The pritchel hole is round and permits slugs of metal to pass through when holes are punched in the stock. swage blocks. 300. No. sledges. 150 weighs 150 lb). bottom. and a vise are used in forging operations. (102 mm) back from the table to provide edges where stock can be bent without danger of cutting it. flatters.(2) The edges of an anvil are rounded for about 4. although steel pedestals or bolsters are sometimes used. and range in size from No 100 to No.00 in. swages. and other special tools. other tools such as hammers. punches. All other edges are sharp and will cut stock when it is hammered against them. chisels. (3) Anvils are designated by weight (i. The height of the anvil should be adjusted so that the operator’s knuckles will just touch its face when he stands erect with his arms hanging naturally. Other Tools. In addition to the anvil.e. fullers. tongs. The anvil is usually mounted on a heavy block of wood. b..

51). STATIONARY WELDING EQUIPMENT Stationay welding equipment is installed where welding operations are conducted in a fixed location. The oxygen is supplied to the welding stations through a pipe line equipped with station outlets (fig. and wrenches to operate the various connections on the cylinders. Oxygen.CHAPTER 5 WELDING AND CUTTING EQUIPMENT
Section I. gloves to protect the hands. 5-2. OXYACETYLENE WELDING EQUIPMENT
5-1. a method to light the torch. The regulator and manifold control the pressure and the flow together (fig. Oxygen and acetylene are provided in the welding area as outlined below. Oxygen is obtained from a number of cylinders manifolded and equipped with a master regulator.
. 5-2). a. GENERAL The equipment used for oxyacetylene welding consists of a source of oxygen and a source of acetylene from a portable or stationary outfit. Other equipment requirements include suitable goggles for eye protection. and torches. regulators. along with a cutting attachment or a separate cutting torch.

.

Acetylene is obtained either from acetylene cylinders set up as shown in figure 5-3. Acetylene. or an acetylene generator (fig.
. 5-4). The acetylene is supplied to the welding stations through a pipe line equipped with station outlets as shown in figure 5-2.b.

.

5-5). Acetylene is colorless.5-3. and necessary wrenches. A metal toolbox. fluxes. generated by the action of calcium carbide. provides storage space for torch tips. goggles. but has a distinctive odor that can be easily detected. a. and hoses (fig. The trucks are equipped with a platform to support two large size cylinders. The cylinders are secured by chains attached to the truck frame. a gray stonelike substance.
5-4. This equipment may be temporarily secured on the floor or mounted on an all welded steel truck. regulators. PORTABLE WELDING EQUIPMENT The portable oxyacetylene welding outfit consists of an oxygen cylinder and an acetylene cylinder with attached valves. gauges. and water in a generating unit. gloves. welded to the frame.
. ACETYLENE GENERATOR NOTE Acetylene generator equipment is not a standard included in this manual for information only. Acetylene is a fuel gas composed of carbon and hydrogen (C2H2).

flammable gas composed of carbon and hydrogen. Acetylene burns in the air with an intensely hot. Acetylene. 5-5.5 hours. can break down from heat or shock. The generator shown in figure 5–4 is a commonly used commercial type. CAUTION Although acetylene is nontoxic. if compressed to 15 psi (103. and possibly explode. and if present in a sufficiently high concentration. Avoid exposing filled cylinders to heat. the calcium carbide is added to the water through a hopper mechanism at a rate which will maintain a working pressure of approximately 15 psi (103. the output for this load is approximately 300 cu ft per hour for 4.5 hours. It is slightly lighter than air. yellow. and a slight shock can cause it to explode spontaneously. Although acetylene is stable under low pressure. luminous. with suitable welding equipment and proper precautions. it becomes unstable. precautions must be taken to prevent excessive pressures in the generator which might cause fires or explosions. In the operation of the generator. 5850°F (3232°C) for a neutral flame. furnaces.4 kPa). CAUTION Since considerable heat is given off during the reaction. or sparks (from a torch). containing from 2 to 80 percent acetylene by volume. A sludge. e. Heat or shock can cause acetylene under pressure to explode. manufactured by the reaction of water and calcium carbide. a.b. Acetylene is a colorless. acetylene becomes self-explosive. is an asphyxiant in that it replaces oxygen and can produce suffocation. Avoid striking the cylinder against other objects and creating sparks. This amount of material will generate 4. b. stored in a free state under pressure greater than 15 psi (103. produces an oxyacetylene flame with inner. However. radiators. welding. will explode when ignited.4 kPa). Mixtures of acetylene and air. for an oxidizing flame. d. open fires. smoky flame. consisting of hydrated or slaked lime. when burned with oxygen. ACETYLENE CYLINDERS WARNING Acetylene.5 cu ft of acetylene per pound. of water. cone tip temperatures of approximately 6300°F (3482°C). it is an anesthetic. c. A double rated generator uses 300 lb of finer sized calcium carbide fed through a special hopper and will deliver 600 cu ft of acetylene per hour for 2. Under pressure of 29.4 psi (203) kPa). A pressure regulator is a built-in part of this equipment. A single rated 300-lb generator uses 300 lb of calcium carbide and 300 gal. settles in the bottom of the generator and is removed by means of a sludge outlet. acetylene can be safely burned with oxygen for heating.4 kPa). To avoid shock when transporting
. and cutting purposes. and 5700°F (3149°C) for a carburizing flame.

1 cu ft per hour. Acetone. or portland cement. 5-6) are filled with porous materials such as balsa wood. which then absorbs the acetylene. The porous material acts as a large sponge which absorbs the acetone. When more than 32. 100. is added to the cylinder until about 40 percent of the porous material is saturated. To prevent drawing off of acetone and consequent impairment of weld quality and damage to the welding equipment. acetylene is contained in three common cylinders with capacities of 1. acetylene cylinders (fig. In order to decrease the size of the open spaces in the cylinder. Acetylene can be compressed into cylinders when dissolved in acetone at pressures up to 250 psi (1724 kPa). or 32.
. a colorless. do not draw acetylene from a cylinder at continuous rates in volumes greater than 1/7 of the rated capacity of the cylinder. Acetylene must not be drawn off in volumes greater than 1/7 of the cylinder’s rated capacity. roll. corn pith. the cylinder manifold system must be used. the volume of acetone increases as it absorbs the acetylene. c. while acetylene. or slide them on their sides. and 300 cu ft. 60. do not drag. d. In this process.cylinders. decreases in volume. or about 275 cu ft per hour.1 cu ft per hour are required. being a gas.
CAUTION Do not fill acetylene cylinders at a rate greater than 1/7 of their rated capacity. flammable liquid. For welding purposes. charcoal.

air is compressed and cooled to a point where the gases become liquid. These stems can be fitted with a cylinder wrench and opened or closed when the cylinder is in use. Production of Oxygen. The regulator inlet connection gland fits against the face of the threaded cylinder connection. 5-6) which have a small hole through the center. or releases at 500 psi (3448 kPa). are then further purified and compressed into cylinders for use. The atmosphere is made up of approximately 21 parts of oxygen and 78 parts of nitrogen. odorless gas that is slightly heavier than air. The brass acetylene cylinder valves have squared stainless steel valve stems. discoloration of copper. This hole is filled with a metal alloy which melts at approximately 212°F (100°C). and the corrosion of aluminum are all due to the action of atmospheric oxygen. having been separated. WARNING Acetylene which may accumulate in a storage room or in a confined space is a fire arid explosion hazard. and the union nut draws the two surfaces together. Acetylene cylinders are equipped with safety plugs (fig. It also has the most concentrated flame. nitrogen in a gaseous form is given off first. known as oxidation. when used with oxygen. In its free state. Acetylene. The plug hole is too small to permit a flame to burn back into the cylinder if escaping acetylene is ignited. but produces less gross heat of combustion than the liquid petroleum gases and the synthetic gases. produces the highest flame temperature of any of the fuel gases. h. Whenever the threads on the valve connections are damaged to a degree that will prevent proper assembly to the regulator. 5-6) screws onto the valve to prevent damage during shipment or storage. The liquid air process is by far the most widely used to produce oxygen. General.e. g. OXYGEN AND ITS PRODUCTION a. oxygen is one of the most common elements. Oxygen is a colorless. When a cylinder is overheated. using a soap solution. b. Rusting of ferrous metals. The outlet of the valve is threaded for connection to an acetylene pressure regulator by means of a union nut. Oxygen is obtained commercially either by the liquid air process or by the electrolytic process. As the temperature of the liquid air rises. since its boiling point is lower than that of liquid oxygen. All acetylene cylinders should be checked. the cylinder should be marked and set aside for return to the manufacturer. These gases. It is nonflammable but will support combustion with other elements. the plug will melt and permit the acetylene to escape before dangerous pressures can be developed.
. (1) In the liquid air process. f. for leakage at the valves and safety fuse plugs. tasteless. A protective metal cap (fig. 5-6. the remainder being rare gases.

and a low melting point safety fuse plug and disk. and is especially dangerous in the presence of oil and grease. Attached equipment provided by the oxygen supplier consists of an outlet valve. Each gas is collected and compressed into cylinders for use.(2) In the electrolytic process. Oxygen cylinders and apparatus should not be handled with oily hands or oily gloves. Oil and grease in the presence of oxygen may spontaneously ignite and burn violently or explode. Combustibles should be kept away from oxygen. valves. 5-7. a removable metal cap for the protection of the valve. oxygen cylinders undergo extensive testing prior to their release for work. The oxygen collects at the positive terminal and the hydrogen at the negative terminal.790 kPa) and a temperature of 70°F (21°C). and other hose apparatus. water is broken down into hydrogen and oxygen by the passage of an electric current. regulators.
. A typical oxygen cylinder is shown in figure 5-7. OXYGEN CYLINDER CAUTION Always refer to oxygen as oxygen. Oxygen should never be used in any air tools or for any of the purposes for which compressed air is normally used. and must be periodically tested thereafter. The cylinder is fabricated from a single plate of high grade steel so that it will have no seams and is heat treated to achieve maximum strength. Because of their high pressure. including the cylinder. never as air. Pure oxygen will support and accelerate combustion of almost any material. It is made of steel and has a capacity of 220 cu ft at a pressure of 2000 psi (13.

b. and balancing springs.
.90 to 172. Pressure gauges are provided to show the pressure in the cylinder or pipe line and the working pressure. Most regulators in use are either the single stage or the two stage type. a valve seat to close off the nozzle. Single Stage Oxygen Regulator. Some types have a relief valve and an inlet filter to exclude dust and dirt. 5-8) has a nozzle through which the high pressure gas passes. A gas pressure regulator will automatically deliver a constant volume of gas to the torch at the adjusted working pressure. OXYGEN AND ACETYLENE REGULATORS a. General. The gases compressed in oxygen and acetylene cylinders are held at pressures too high for oxyacetylene welding.38 kPa). acetylene. Regulators reduce pressure and control the flow of gases from the cylinders. The single stage oxygen regulator mechanism (fig. The single stage oxygen regulator reduces the cylinder pressure of a gas to a working pressure in one step.169 kPa). and liquid petroleum fuel gases are of different construction. The pressure in an oxygen cylinder can be as high as 2200 psi (15. They must be used only for the gas for which they were designed. The pressure of acetylene in an acetylene cylinder can be as high as 250 psi (1724 kPa).5-8. NOTE The regulators for oxygen. Check valves must be installed between the torch hoses and the regulator to prevent flashback through the regulator. which must be reduced to a working pressure of 1 to 25 psi (6.

the working pressure falls as the cylinder pressure falls. which compensates for the pressure of the gas against the diaphragm. (2) The oxygen enters the regulator through the high pressure inlet connection and passes through a glass wool filter. (1) The regulator consists of a flexible diaphragm. which closes off the nozzle. which controls a needle valve between the high pressure zone and the working zone. c. which is on the inlet side of the regulator. which is on the outlet side of the regulator. which removes dust and dirt. and an adjusting screw. Operation of Single Stage Oxygen Regulator. Pressure is applied to the adjusting spring by turning the adjusting screw. The needle valve is on the side of the diaphragm exposed to high gas pressure while the compression spring and adjusting screw are on the opposite side in a zone vented to the atmosphere. The low or working pressure gauge. is not raised until the adjusting screw is turned in. is graduated from 0 to 500 psi. The seat. The high pressure gauge. is graduated from 0 to 3000 psi. the working pressure must be adjusted at intervals during welding operations when using a single stage oxygen regulator. a compression spring. which occurs gradually as gas is withdrawn.NOTE In operation. For this reason. The oxygen regulator controls and reduces the oxygen pressure from any standard commercial oxygen cylinder containing pressures up to 3000 psi. which bears down on the rubber
.

the pressure is reduced from cylinder pressure to intermediate pressure. even if the torch needle valve is open. Oxygen is then allowed to flow into the low pressure chamber of the regulator. 5–9) is similar in operation to the one stage regulator. and depends on the position of the regulator adjusting screw. Because of the two stage pressure control. and pressure adjustment during welding operations is not required. acetylene manifold. Pressure is increased by turning the adjusting screw to the right and decreased by turning this screw to the left. The two stage oxygen regulator (fig.4 kPa) for acetylene and approximately 200 psi (1379 kPa) for oxygen. When the stirrup is forced downward. (3) Regulators used at stations to which gases are piped from an oxygen manifold. On the low pressure side the pressure is reduced from intermediate pressure to work pressure. A certain set pressure must be maintained in the low pressure chamber of the regulator so that oxygen will continue to be forced through the orifices of the torch.
e.
. The diaphragm presses downward on the stirrup and overcomes the pressure on the compensating spring. This pressure is indicated on the working pressure gage of the regulator. the working pressure is held constant. Acetylene Regulator. or acetylene generator have only one low pressure gage because the pipe line pressures are usually set at 15 psi (103. The oxygen then passes through the regulator outlet and the hose to the torch. the passage through the nozzle is open. but reduces pressure in two steps. On the high pressure side.diaphragm.

5 kPa). The tubes and handle are of seamless hard brass. The welding tips may or may not have separate injectors designed integrally with each tip. 5-10). For a description and the different sized tips. The high pressure gage. stainless steel. Any change in oxygen flow will produce relative change in acetylene flow so that the proportion of the two gases remains constant. The oxyacetylene welding torch is used to mix oxygen and acetylene in definite proportions. on the outlet side of the regulator. In addition. there are two tubes.
. the other for acetylene. on the inlet side of the regulator. The low pressure gage. inlet nipples for the attachment of hoses. b. is graduated from 0 to 30 psi (207 kPa). Types of Torches. see paragraph 5-10. Acetylene should not be used at pressures exceeding 15 psi (103. (1) In the low pressure or injector type (fig. and a mixing head. but will not withstand such high pressures. The torch consists of a handle or body which contains the hose connections for the oxygen and the fuel gas. copper-nickel alloy.895 kPa). 5-9.4 kPa). the acetylene pressure is less than 1 psi (6. OXYACETYLENE WELDING TORCH a. and the equal pressure type. one for adjusting the flew of oxygen and one for acetylene.CAUTION Acetylene should never be used at pressures exceeding 15 psi (103. General. It also controls the volume of these gases burning at the welding tip. is graduated from 0 to 500 psi (3447.5 kPa). The torch also has two needle valves. The acetylene regulator design is generally the same as that of the oxygen regulator. which produces the required type of flame. This regulator controls the acetylene pressure from any standard commercial cylinder containing pressures up to 500 psi (3447. the low pressure or injector type. a tip. This is accomplished by designing the mixer in the torch to operate on the injector principle. There are two general types of welding torches. A jet of high pressure oxygen is used to produce a suction effect to draw in the required amount of acetylene. one for oxygen.4 kPa). and a handle.

(2) The equal pressure torch (fig. 5-11) is designed to operate with equal pressures for the oxygen and acetylene. The pressure ranges from 1 to 15 psi (6.895 to 103.4 kPa). This torch has certain advantages over the low pressure type. It can be more readily adjusted, and since equal pressures are used for each gas, the torch is less susceptible to flashbacks.

5-10. WELDING TIPS AND MIXERS a. The welding tips (fig. 5-10 and 5-11) are made of hard drawn electrolytic or 95 percent copper and 5 percent tellurium. They are made in various and types, some having a one-piece tip either with a single orifice or a of orifices. The diameters of the tip orifices differ in order to control the quantity of heat and the type of flame. These tip sizes are designated by numbers which are

arranged according to the individual manufacturer’s system. Generally, the smaller the number, the smaller the tip orifice. b. Mixers (fig. 5-10 and 5-11) are frequently provided in tip tier assemblies which assure the correct flow of mixed gases for each size tip. In this tip mixer assembly, the mixer is assembled with the tip for which it has been drilled and then screwed onto the torch head. The universal type mixer is a separate unit which can be used with tips of various sizes. 5-11. HOSE a. The hoses used to make the connection between are made especially for this purpose. (1) Hoses are built to withstand high internal the regulators and the torch pressures. (2) They are strong, nonporous, light, and flexible to permit easy manipulation of the torch. (3) The rubber used in the manufacture of hose is chemically treated to remove free sulfur to avoid possible spontaneous combustion. (4) The hose is not impaired by prolonged exposure to light. CAUTION Hose should never be used for one gas if it was previously used for another. b. Hose identification and composition. (1) In North America, the oxygen hose is green and the acetylene hose is red. In Europe, blue is used for oxygen and orange for acetylene. Black is sometimes also used for oxygen. (2) The hose is a rubber tube with braided or wrapped cotton or rayon reinforcements and a rubber covering. For heavy duty welding and cutting operations, requiring 1/4-to 1/2-in. internal diameter hose, three to five plies of braided or wrapped reinforcements are used. One ply is used in the 1/8-to 3/16-in. hose for light torches. c. Hoses are provided with connections at each end so that they may be connected to their respective regulator outlet and torch inlet connections. To prevent a dangerous interchange of acetylene and oxygen hoses, all threaded fittings used for the acetylene hook up are left hand, and all threaded fittings for the oxygen hook up are right hand. Notches are also placed on acetylene fittings to prevent a mixup. d. Welding and cutting hoses are obtainable as a single hose for each gas or with the hoses bonded together along their length under a common outer rubber jacket. The latter type prevents the hose from kinking or becoming tangled during the welding operation.

5-12. SETTING UP THE EQUIPMENT WARNING Always have suitable fire extinguishing equipment at hand when doing any welding. When setting up welding and cutting equipment, it is important that all operations be performed systematically in order to avoid mistakes and possible trouble. The setting up procedures given in a through d below will assure safety to the operator and the apparatus. a. Cylinders. WARNING Do not stand facing cylinder valve outlets of oxygen, acetylene, or other compressed gases when opening them. (1) Place the oxygen and the acetylene cylinders on a level floor (if they are not mounted on a truck), and tie them firmly to a work bench, post, wall, or other secure anchorage to prevent their being knocked or pulled over. (2) Remove the valve protecting caps. (3) "Crack" both cylinder valves by opening first the acetylene and then the oxygen valve slightly for an instant to blow out any dirt or foreign matter that may have accumulated during shipment or storage. (4) Close the valves and wipe the connection seats with a clean cloth. b. Pressure Regulators. (1) Check the regulator fittings for dirt and obstructions. Also check threads of cylinders and regulators for imperfections. (2) Connect the acetylene regulator to the acetylene regulator and the oxygen regulator to the oxygen cylinder. Use either a regulator wrench or a close fitting wrench and tighten the connecting nuts sufficiently to prevent leakage. (3) Check hose for burns, nicks, and bad fittings. (4) Connect the red hose to the acetylene regulator and the green hose to the oxygen regulator. Screw the connecting nuts tightly to insure leakproof seating. Note that the acetylene hose connection has left hand threads. WARNING

If it is necessary to blow out the acetylene hose, do it in a well ventilated place which is free of sparks, flame, or other sources of ignition. (5) Release the regulator screws to avoid damage to the regulators and gages. Open the cylinder valves slowly. Read the high pressure gages to check the cylinder gas pressure. Blow out the oxygen hose by turning the regulator screw in and then release the regulator screw. Flashback suppressors must be attached to the torch whenever possible. c. Torch. Connect the red acetylene hose to the torch needle valve which is stamped "AC or flashback suppressor". Connect the green oxygen hose to the torch needle valve which is stamped "OX or flashback suppressor". Test all hose connections for leaks at the regulators and torch valves by turning both regulators’ screws in with the torch needle valves closed. Use a soap and water solution to test for leaks at all connections. Tighten or replace connections where leaks are found. Release the regulator screws after testing and drain both hose lines by opening the torch needle valves. Slip the tip nut over the tip, and press the tip into the mixing head. Tighten by hand and adjust the tip to the proper angle. Secure this adjustment by tightening with the tip nut wrench. WARNING Purge both acetylene and oxygen lines (hoses) prior to igniting torch. Failure to do this can cause serious injury to personnel and damage to the equipment. d. Adjustment of Working Pressure. Adjust the acetylene working pressure by opening the acetylene needle valve on the torch and turning the regulator screw to the right. Then adjust the acetylene regulator to the required pressure for the tip size to be used (tables 5-1 and 5-2). Close the needle valve. Adjust the oxygen working pressure in the same manner.

5-13. SHUTTING DOWN WELDING APPARATUS a. Shut off the gases. Close the acetylene valve first, then the oxygen valve on the torch. Then close the acetylene and oxygen cylinder valves. b. Drain the regulators and hoses by the following procedures: (1) Open the torch acetylene valve until the gas stops flowing and the gauges read zero, then close the valve. (2) Open the torch oxygen valve to drain the oxygen regulator and hose. When gas stops flowing and the gauges read zero, close the valve. (3) When the above operations are performed properly, both high and low pressure gauges on the acetylene and oxygen regulators will register zero. c. Release the tension on both regulator screws by turning the screws to the left until they rotate freely. d. Coil the hoses without kinking them and suspend them on a suitable holder or hanger. Avoid upsetting the cylinders to which they are attached. 5-14. REGULATOR MALFUNCTIONS AND CORRECTIONS a. Leakage of gas between the regulator seat and the nozzle is the principal problem encounter with regulators. It is indicated by a gradual increase in pressure on the working pressure gauge when the adjusting screw is fully released or is in position after adjustment. This defect, called "creeping regulator", is caused by bad valve seats or by foreign matter lodged between the seat and the nozzle. WARNING

Regulators with leakage of gas between the regulator seat and the nozzle must be replaced immediately to avoid damage to other parts of the regulator or injury to personnel. With acetylene regulators, this leakage is particularity dangerous because acetylene at high pressure in the hose is an explosion hazard. b. The leakage of gas, as described above, can be corrected as outlined below: (1) Remove and replace the seat if it is worn, cracked, or otherwise damaged. (2) If the malfunction is caused by fouling with dirt or other foreign matter, clean the seat and nozzle thoroughly and blow out any dust or dirt in the valve chamber. c. The procedure for removing valve seats and nozzles will vary with the make or design. d. Broken or buckled gage tubes and distorted or buckled diaphragms are usually caused by backfire at the torch, leaks across the regulator seats, or by failure to release the regulator adjusting screw fully before opening the cylinder valves. e. Defective bourdon tubes in the gages are indicated by improper action of the gages or by escaping gas from the gage case. Gages with defective bourdon tubes should be removed and replaced with new gages. Satisfactory repairs cannot be made without special equipment. f. Buckled or distorted diaphragms cannot be adjusted properly and should be replaced with new ones. Rubber diaphragms can be replaced easily by removing the spring case with a vise or wrench. Metal diaphragms are sometimes soldered to the valve case and their replacement is a factory or special repair shop job. Such repairs should not be attempted by anyone unfamiliar with the work. 5-15. TORCH MALFUNCTIONS AND CORRECTIONS WARNING Defects in oxyacetylene welding torches which are sources of gas leaks must be corrected immediately, as they may result in flashbacks or backfires, with resultant injury to the operator and/ or damage to the welding apparatus. a. General. Improved functioning of welding torches is usually due to one or more of the following causes: leaking valves, leaks in the mixing head seat, scored or out-of-round welding tip orifices, clogged tubes or tips, and damaged inlet connection threads. Corrective measures for these common torch defects are described below. b. Leaking Valves. (1) Bent or worn valve stems should be replaced and damaged seats should be refaced.

(2) Loose packing may be corrected by tightening the packing nut or by installing new packing and then tightening the packing nut. CAUTION This work should be done by the manufacturer because special reamers are required for trueing these seats. c. Leaks in the Mixing Heads. These are indicated by popping out of the flame and by emission of sparks from the tips accompanied by a squealing noise. Leaks in the mixing head will cause improper mixing of the oxygen and acetylene causing flashbacks. A flashback causes the torch head and handle to suddenly become very hot. Repair by reaming out and trueing the mixing head seat. d. Scored or Out-of-Round Tip Orifices. Tips in this condition cause the flame to be irregular and must be replaced. e. Clogged Tubes and Tips. (1) Carbon deposits caused by flashbacks or backfire, or the presence of foreign matter that has entered the tubes through the hoses will clog tubes. If the tubes or tips are clogged, greater working pressures will be needed to produce the flame required. The flame produced will be distorted. (2) The torch should be disassembled so that the tip, mixing head, valves, and hose can be cleaned and cleaned out with compressed air at a pressure of 20 to 30 psi (137.9 to 206.85 kPa). (3) The tip and mixing head should be cleaned either with a cleaning drill or with soft copper or brass wire, and then blown out with compressed air. The cleaning drills should be approximately one drill size smaller than the tip orifice to avoid enlarging the orifice during cleaning. WARNING Damages inlet connection threads may cause fires by ignition of the leaking gas, resulting in injury to the welding operator and/or damage to the equipment. f. Damaged Inlet Connection Threads. Leaks due to damaged inlet connection threads can be detected by opening the cylinder valves and keeping the needle valves closed. Such leaks will cause the regulator pressure to drop. Also, if the threads are damaged, the hose connection at the torch inlet will be difficult or impossible to tighten. To correct this defect, the threads should be recut and the hose connections thoroughly cleaned.

Section II. OXYACETYLENE CUTTING EQUIPMENT

5-16. CUTTING TORCH AND OTHER CUTTING EQUIPMENT a. The cutting torch (fig. 5-12), like the welding torch, has a tube for oxygen and one for acetylene. In addition, there is a tube for high pressure oxygen, along with a cutting tip or nozzle. The tip (fig. 5-13) is provided with a center hole through which a jet of pure oxygen passes. Mixed oxygen and acetylene pass through holes surrounding the center holes for the preheating flames. The number of orifices for oxyacetlylene flames ranges from 2 to 6, depending on the purpose for which the tip is used. The cutting torch is controlled by a trigger or lever operated valve. The cutting torch is furnished with interchangeable tips for cutting steel from less than 1/4 in. (6.4 mm) to more than 12.0 in. (304.8 mm) in thickness.

b. A cutting attachment fitted to a welding torch in place of the welding tip is shown in figure 514.

c. In order to make uniformly clean cuts on steel plate, motor driven cutting machines are used to support and guide the cutting torch. Straight line cutting or beveling is accomplished by guiding the machine along a straight line on steel tracks. Arcs and circles are cut by guiding the machine with a radius rod pivoted about a central point. Typical cutting machines in operation are shown in figures 5-15 and 5-16.

d. There is a wide variety of cutting tip styles and sizes available to suit various types of work. The thickness of the material to be cut generally governs the selection of the tip. The cutting oxygen pressure, cutting speed, and preheating intensity should be controlled to produce narrow, parallel sided kerfs. Cuts that are improperly made will produce ragged, irregular edges with adhering slag at the bottom of the plates. Table 5-3 identifies cutting tip numbers, gas pressures, and hand-cutting speeds used for cutting mild steel up to 12 in. (304.8 mm) thick.

5-17. OPERATION OF CUTTING EQUIPMENT

a. Attach the required cutting tip to the torch and adjust the oxygen and acetylene pressures in accordance with table 5-3. NOTE The oxygen and acetylene gas pressure settings listed are only approximate. In actual use, pressures should be set to effect the best metal cut. b. Adjust the preheating flame to neutral. c. Hold the torch so that the cutting oxygen lever or trigger can be operated with one hand. Use the other hand to steady and maintain the position of the torch head to the work. Keep the flame at a 90 degree angle to work in the direction of travel. The inner cones of the preheating flames should be about 1/16 in. (1.6 mm) above the end of the line to be cut. Hold this position until the spot has been raised to a bright red heat, and then slowly open the cutting oxygen valve. d. If the cut has been started properly, a shower of sparks will fall from the opposite side of the work. Move the torch at a speed which will allow the cut to continue penetrating the work. A good cut will be clean and narrow. e. When cutting billets, round bars, or heavy sections, time and gas are saved if a burr is raised with a chisel at the point where the cut is to start. This small portion will heat quickly and cutting will start immediately. A welding rod can be used to start a cut on heavy sections. When used, it is called a starting rod.

Section III. ARC WELDING EQUIPMENT AND ACCESSORIES
5-18. GENERAL In electric welding processes, an arc is produced between an electrode and the work piece (base metal). The arc is formed by passing a current between the electrode and the workpiece across the gap. The current melts the base metal and the electrode (if the electrode is a consumable type), creating a molten pool. On solidifying, the weld is formal. An alternate method employs a nonconsumable electrode, such as a tungsten rod. In this case, the weld is formed by melting and solidifying the base metal at the joint. In some instances, additional metal is required, and is added to the molten pool from a filler rod. Electrical equipment required for arc welding depends on the source from which the electric power is obtained. If the power is obtained from public utility lines, one or more of the following devices are required: transformers (of which there are several types), rectifiers, motor generators, and control equipment. If public utility power is not available, portable generators driven by gasoline or diesel engines are used. 5-19. DIRECT CURRENT ARC WELDING MACHINES

a. The direct current welding machine has a heavy duty direct current generator (fig. 5-17). The generators are made in six standardized ratings for general purposes as described below:

(1) The machines rated 150 and 200 amperes, 30 volts, are used for light shielded metalarc welding and for gas metal-arc welding. They are also used for general purpose job shop work. (2) The machines rated 200, 300, and 400 amperes, 40 volts, used for general welding purposes by machine or manual application. (3) Machines rated 600 amperes, 40 volts, are used for submerged arc welding and for carbon-arc welding. b. The electric motors must commonly used to drive the welding generators are 220/440 volts, 3 phase, 60 cycle. The gasoline and diesel engines should have a rated horsepower in excess of the rated output of the generator. This will allow for the rated overload capacity of the generator and for the power required to operate the accessories of the engine. The simple equation HP = 1.25P/746 can be used; HP is the engine horsepower and P is the generator rating in watts. For example, a 20 horsepower engine would be used to drive a welding generator with a rated 12 kilowatt output. c. In most direct current welding machines, the generator is of the variable voltage type, and is arranged so that the voltage is automatically adjusted to the demands of the arc. However, the voltage may be set manually with a rheostat.

d. The welding current amperage is also manually adjustable, and is set by means of a selector switch or series of plug receptacles. In either case, the desired amperage is obtained by tapping into the generator field coils. When both voltage and amperage of the welding machine are adjustable, the machine is known as dual control type. Welding machines are also manufactured in which current controls are maintained by movement of the brush assembly. e. A direct current welding machine is described in TM 5-3431-221-15, and is illustrated in figure 5-18.

f. A maintenance schedule should be set up to keep the welding machine in good operating condition. The machine should be thoroughly inspected every 3 months and blown free of dust with clean, dry, compressed air. At least once each year, the contacts of the motor starter switches and the rheostat should be cleaned and replaced if necessary. Brushes should be inspected frequently to see if they are making proper contact on the commutator, and that they move freely in the brush holders. Clean and true the commutator with sandpaper or a commutator stone if it is burned or roughened. Check the bearings twice a year. Remove all the old grease and replace it with new grease. g. Direct current rectifier type welding machines have been designed with copper oxide, silicon, or selenium dry plates. These machines usually consist of a transform to reduce the power line voltage to the required 220/440 volts, 3 phase, 60 cycle input current; a reactor for adjustment of the current; and a rectifier to change the alternating current to direct current. Sometimes another reactor is used to reduce ripple in the output current. 5-20. ALTERNATING CURRENT ARC WELDING MACHINES

a. Most of the alternating current arc welding machines in use are of the single operator, static transformer type (fig. 5-19). For manual operation in industrial applications, machines having 200, 300, and 400 amphere ratings are the sizes in general use. Machines with 150 ampere ratings are sometimes used in light industrial, garage and job shop welding.

b. The transformers are generally equipped with arc stabilizing capacitors. Current control is provided in several ways. One such method is by means of an adjustable reactor in the output circuit of the transformer. In other types, internal reactions of the transformer are adjustable. A handwheel, usually installed on the front or the top of the machine, makes continuous adjustment of the output current, without steps, possible. c. The screws and bearings on machines with screw type adjustments should be lubricated every 3 months. The same lubrication schedule applies to chain drives. Contacts, switches, relays, and plug and jack connections should be inspected every 3 months and cleaned or replaced as required. The primary input current at no load should be measured and checked once a year to ensure the power factor connecting capacitors are working, and that input current is as specified on the nameplate or in the manufacturer’s instruction book. 5-21. GAS TUNGSTEN-ARC WELDING (GTAW) EQUIPMENT (TIG) a. General. In tungsten inert gas (TIG) welding, (also known as GTAW), an arc is struck between a virtually nonconsumable tungsten electrode and the workpiece. The heat of the arc causes the edges of the work to melt and flow together. Filler rod is often required to fill the joint. During the welding operation, the weld area is shielded from the atmosphere by a blanket of inert argon gas. A steady stream of argon passes through the torch, which pushes the air away from the welding area and prevents oxidation of the electrode, weld puddle, and heat affected zone.

b. Equipment. (1) The basic equipment requirements for manual TIG welding are shown in figure 5-20. Equipment consists of the welding torch plus additional apparatus to supply electrical power, shielding gas, and a water inlet and outlet. Also, personal protective equipment should be worn to protect the operator from the arc rays during welding operations.

NOTE Different types of TIG welding equipment are available through normal supply channels. Watercooled torches and air-cooled torches are both available. Each type carries different amperage ratings. Consult the appropriate manual covering the type torch used. (2) Argon is supplied in steel cylinders containing approximately 330 cu ft at a pressure to 2000 psi (13,790 kPa). A single or two stage regulator may be used to control the gas flow. A specially designed regulator containing a flowmeter, as shown in figure 5-21, may be used. The flowmeter provides better adjustment via flow control than the single or two stage regulator and is calibrated in cubic feet per hour (cfh). The correct flow of argon to the torch is set by turning the adjusting screw on the regulator. The rate of flow depends on the kind and thickness of the metal to be welded.

(3) Blanketing of the weld area is provided by a steady flow of argon gas through the welding torch (fig. 5-22). Since argon is slightly more than 1-1/3 times as heavy as air, it pushes the lighter air molecules aside, effectively preventing oxidation of the welding electrode, the molten weld puddle, and the heat affected zone adjacent to the weld bead.

(4) The tremendous heat of the arc and the high current often used usually necessitate water cooling of the torch and power cable (fig. 5-22). The cooling water must be clean; otherwise, restricted or blocked passages may cause excessive overheating and damage to the equipment. It is advisable to use a suitable water strainer or filter at the water supply source. If a self-contained unit is used, such as the one used in the field (surge tank) where the cooling water is recirculated through a pump, antifreeze is required if the unit is to be used outdoors during the winter months or freezing weather. Some TIG welding torches require less than 55 psi (379 kPa) water pressure and will require a water regulator of some type. Check the operating manual for this information. c. Nomenclature of Torch (fig. 5-22). (1) Cap. Prevents the escape of gas from the top of the torch and locks the electrode in place. (2) Collet. Made of copper; the electrode fits inside and when the cap is tightened, it squeezes against the electrode and leeks it in place. (3) Gas orifice nut. Allows the gas to escape. (4) Gas nozzle. Directs the flew of shielding gas onto the weld puddle. Two types of nozzles are used; the one for light duty welding is made of a ceramic material, and the one for heavy duty welding is a copper water-cooled nozzle. (5) Hoses. Three plastic hoses, connected inside the torch handle, carry water, gas, and the electrode power cable. 5-22. GAS METAL-ARC WELDING (GMAW) EQUIPMENT a. General. GMAW is most commonly referred to as "MIG" welding, and the following text will use "MIG" or "MIG welding" when referring to GMAW. MIG welding is a process in which a consumable, bare wire electrode is fed into a weld at a controlled rate of speed, while a blanket of inert argon gas shields the weld zone from atmospheric contamination. In addition to the three basic types of metal transfer which characterize the GMAW process, there are several variations of significance. (1) Pulsed spray welding. Pulsed spray welding is a variation of the MIG welding process that is capable of all–position welding at higher energy levels than short circuiting arc welding. The power source provides two current levels; a steady "background" level, which is too low to produce spray transfer; and a "pulsed peak" current, which is superimposed upon the background current at a regulated interval. The pulse peak is well above the transition current, and usually one drop is transferred during each pulse. The combination of the two levels of current produces a steady arc with axial spray transfer at effective welding currents below those required for conventional spray arc welding. Because the heat input is lower, this variation in operation is capable of welding thinner sections than are practical with the conventional spray transfer.

(2) Arc spot welding. Gas metal arc spot welding is a method of joining similar to resistance spot welding and riveting. A variation of continuous gas metal arc welding, the process fuses two pieces of sheet metal together by penetrating entirely through one piece into the other. No joint preparation is required other than cleaning of the overlap areas. The welding gun remains stationary while a spot weld is being made. Mild steel, stainless steel, and aluminum are commonly joined by this method. (3) Electrogas welding. The electrogas (EG) variation of the MIG welding process is a fully automatic, high deposition rate method for the welding of butt, corner, and T-joints in the vertical position. The eletrogas variation essentially combines the mechanical features of electroslag welding (ESW) with the MIG welding process. Water-coded copper shoes span the gap between the pieces being welded to form a cavity for the molten metal. A carriage is mounted on a vertical column; this combination provides both vertical and horizontal movement. Welding head, controls, and electrode spools are mounted on the carriage. Both the carriage and the copper shoes move vertically upwards as welding progresses. The welding head may also be oscillated to provide uniform distribution of heat and filler metal. This method is capable of welding metal sections of from 1/2 in. (13 mm) to more than 2 in. (5.08 an) in thickness in a single pass. Deposition rates of 35 to 46 lb (16 to 21 kg) per hour per electrode can be achieved. b. MIG Equipment. NOTE Different types of MIG welding equipment are available through normal supply channels. Manuals for each type must be consulted prior to welding operations. (1) The MIG welding unit is designed for manual welding with small diameter wire electrodes, using a spool-on-gun torch. The unit consists of a torch (fig. 5-23), a voltage control box, and a welding contractor (fig. 5-24). The torch handle contains a complete motor and gear reduction unit that pulls the welding wire electrode from a 4 in. (102 mm) diameter spool containing 1 lb (0.5 kg) of wire electrode mounted in the rear of the torch.

(2) Three basic sizes of wire electrode maybe used: 3/32 in. (2.38 mm), 3/64 in. (1.19 mm), and 1/16 in. (1.59 mm). Many types of metal may be welded provided the welding wire electrode is of the same composition as the base metal. (3) The unit is designed for use with an ac-dc conventional, constant-current welding power supply. Gasoline engine-driven arc welding machines issued to field units may be used as both a power source and a welding source. c. Nomenclature of Torch. (1) Contact tube (fig. 5-23). This tube is made of copper and has a hole in the center of the tube that is from 0.01 to 0.02 in. (0.25 to 0.51 mm) larger than the size of the wire electrode being used. The contact tube and the inlet and outlet guide bushings must be charged when the size of the wire electrode is changed. The contact tube transfers power from the electrode cable to the welding wire electrode. An insulated lock screw is provided which secures the contact tube in the torch. (2) Nozzle and holder (fig. 5-23). The nozzle is made of copper to dissipate heat and is chrome-plated to reflect the heat. The holder is made of stainless steel and is connected to an insulating material which prevents an arc from being drawn between the nozzle and the ground in case the gun canes in contact with the work. (3) Inlet and outlet guide bushings (fig. 5-23). The bushings are made of nylon for long wear. They must be changed to suit the wire electrode size when the electrode wire is changed. (4) Pressure roll assembly (fig. 5-23). This is a smooth roller, under spring tension, which pushes the wire electrode against the feed roll and allows the wire to be pulled from the spool. A thumbscrew applies tension as required. (5) Motor (fig. 5-23). When the inch button is depressed, the current for running the motor comes from the 110 V ac-dc source, and the rotor pulls the wire electrode from the spool before starting the welding operation. When the trigger is depressed, the actual welding operation starts and the motor pulls the electrode from the spool at the required rate of feed. The current for this rotor is supplied by the welding generator. (6) Spool enclosure assembly (fig. 5-23). This assembly is made of plastic which prevents arc spatter from jamming the wire electrode on the spool. A small window allows the operator to visually check the amount of wire electrode remaining on the spool. NOTE If for any reason the wire electrode stops feeding, a burn-back will result. With the trigger depressed, the welding contactor is closed, thereby allowing the welding current to flow through the contact tube. As long as the wire electrode advances through the tube, an arc will be drawn at

the end of the wire electrode. Should the wire electrode stop feeding while the trigger is still being depressed, the arc will then form at the end of the contact tube, causing it to melt off. This is called burn-back. (7) Welding contactor (fig. 5-24). The positive cable from the dc welding generator is connected to a cable coming out of the welding contactor, and the ground cable is connected to the workpiece. The electrode cable and the welding contactor cable are connected between the welding contactor and voltage control box as shown. (8) Argon gas hose (fig. 5-24). This hose is connected from the voltage control box to the argon gas regulator on the argon cylinder. (9) Electrode cable (fig. 5-24). The electrode cable enters through the welding current relay and connects into the argon supply line. Both then go out of the voltage control box and into the torch in one line. (10) Voltage pickup cable (fig. 5-24). This cable must be attached to the ground cable at the workpiece. This supplies the current to the motor during welding when the trigger is depressed. (11) Torch switch and grounding cables (fig. 5-24). The torch switch cable is connected into the voltage control box, and the torch grounding cable is connected to the case of the voltage control box. 5-23. OPERATING THE MIG a. Starting to Weld. (1) Press the inch button and allow enough wire electrode to emerge from the nozzle until 1/2 in. (13 mm) protrudes beyond the end of the nozzle. With the main line switch "ON" and the argon gas and power sources adjusted properly, the operator may begin to weld. (2) When welding in the open air, a protective shield must be installed to prevent the argon gas from being blown away from the weld zone and allowing the weld to become contaminate. (3) Press the torch trigger. This sends current down the torch switch cable and through the contactor cable, closing the contactor. (4) When the contactor closes, the welding circuit from the generator to the welding torch is completed. (5) At the same time the contactor closes, the argon gas solenoid valve opens, allowing a flow of argon gas to pass out of the nozzle to shield the weld zone.

(6) Lower the welding helmet and touch the end of the wire electrode to the workpiece. The gun is held at a 90 degree angle to the work but pointed at a 10 degree angle toward the line of travel. CAUTION To prevent overloading the torch motor when stopping the arc, release the trigger; never snap the arc out by raising the torch without first releasing the trigger. (7) Welding will continue as long as the arc is maintained and the trigger is depressed. b. Setting the Wire Electrode Feed. (1) A dial on the front of the voltage control box, labeled WELDING CONTROL, is used to regulate the speed of the wire electrode feed. (2) To increase the speed of the wire electrode being fed from the spool, turn the dial counterclockwise. This decreases the amount of resistance across the arc and allows the motor to turn faster. Turning the dial clockwise will increase the amount of resistance, thereby decreasing the speed of wire electrode being fed from the spool. (3) At the instant that the wire electrode touches the work, between 50 and volts dc is generated. This voltage is picked up by the voltage pickup cable shunted back through the voltage control box into a resistor. There it is reduced to the correct voltage (24 V dc) and sent to the torch motor. c. Fuses. (1) Two 10-ampere fuses, located at the front of the voltage control box, protect and control the electrical circuit within the voltage control box. (2) A 1-ampere fuse, located on the front of the voltage control box, protects and controls the torch motor. d. Installing the Wire Electrode. (1) Open the spool enclosure cover assembly, brake, and pressure roll assembly (fig. 523). (2) Unroll the straighten 6 in. (152 mm) of wire electrode from the top of the spool. (3) Feed this straightened end of the wire electrode into the inlet and outlet bushings; then place spool onto the mounting shaft. (4) Close the pressure roller and secure it in place. Press the inch button, feeding the wire electrode until there is 1/2 in. (13 mm) protruding beyond the end of the nozzle.

e. Setting the Argon Gas Pressure. (1) Flip the argon switch on the front of the voltage control panel to the MANUAL position. (2) Turn on the argon gas cylinder valve and set the pressure on the regulator. (3) When the proper pressure is set on the regulator, flip the argon switch to the AUTOMATIC POSITION. (4) When in the MANUAL position, the argon gas continues to flow. When in the AUTOMATIC position, the argon gas flows only when the torch trigger is depressed, and stops flowing when the torch trigger is released. f. Generator Polarity. The generator is set on reverse polarity. When set on straight polarity, the torch motor will run in reverse, withdrawing the wire electrode and causing a severe burn-back. g. Reclaiming Burned-Back Contact Tubes. When the contact tubes are new, they are 5-3/8 in. (137 mm) long. When burn-backs occur, a maximum of 3/8 in. (9.5 mm) may be filed off. File a flat spot on top of the guide tube, place a drill pilot on the contact tube, then drill out the contact tube. For a 3/64 in. (1.2 mm) contact tube, use a No. 46 or 47 drill bit. h. Preventive Maintenance. (1) Keep all weld spatter cleaned out of the inside of the torch. Welding in the vertical or overhead positions will cause spatter to fall down inside the torch nozzle holder and restrict the passage of the argon gas. Keep all hose connections tight. (2) To replace the feed roll, remove the nameplate on top of the torch, the flathead screw and retainer from the feed roll mounting shaft, and the contact ring and feed roll. Place a new feed roll on the feed roll mounting shaft, making certain that the pins protruding from the shaft engage the slots in the feed roll. Reassemble the contact ring and nameplate. 5-24. OTHER WELDING EQUIPMENT a. Cables. Two welding cables of sufficient current carrying capacity with heavy, tough, resilient rubber jackets are required. One of the cables should be composed of fine copper strands to permit as much flexibility as the size of the cable will allow. One end of the less flexible cable is attached to the ground lug or positive side of the direct current welding machine; the other end to the work table or other suitable ground. One end of the flexible cable is attached to the electrode holder and the other end to the negative side of a direct current welding machine for straight polarity. Most machines are equipped with a polarity switch which is used to change the polarity without interchanging the welding cables at the terminals of the machine. For those machines not equipped with polarity switches, for reverse polarity, the cables are reversed at the machine.

b. Electrode Holders. An electrode holder is an insulated clamping device for holding the electrode during the welding operation. The design of the holder depends on the welding process for which it is used, as explained below. (1) Metal-arc electrode holder. This is an insulated clamp in which a metal electrode can be held at any desired angle. The jaws can be opened by means of a lever held in place by a spring (fig. 5-25).

(2) Atomic hydrogen torch. This electrode holder or torch consists of two tubes in an insulated handle, through which both hydrogen gas and electric current flow. The hydrogen is supplied to a tube in the rear of the handle from which it is led into the two current carrying tubes by means of a manifold. One of the two electrode holders is movable, and the gap between this and the other holder is adjusted by means of a trigger on the handle (fig. 5-26).

(3) Carbon-arc electrode holder. This holder is manufactured in three specific types. One type holds two electrodes and is similar in design to the atomic hydrogen torch, but has no gas tubes; a second equipped with a heat shield; the third type is watercooled. c. Accessories. (1) Chipping hammer and wire brush. A chipping hammer is required to loosen scale, oxides and slag. A wire brush is used to clean each weld bead before further welding. Figure 5-27 shows a chipping hammer with an attachable wire brush.

(2) Welding table. A welding table should be of all-steel construction. A container for electrodes with an insulated hook to hold the electrode holder when not in use should be provided. A typical design for a welding table is shown in figure 5-28.

(3) Clamps and backup bars. Workpieces for welding should be clamped in position with C-clamps or other clamp brackets. Blocks, strips, or bars of copper or cast iron should be available for use as backup bars in welding light sheet aluminum and in making certain types of joints. Carbon blocks, fire clay, or other fire-resistant material should also be available. These materials are used to form molds which hold molten metal within given limits when building up sections. A mixture of water, glass, and fire clay or carbon powder can be used for making molds.

d. Goggles. Goggles with green lenses shaped to cover the eye orbit should be available to provide glare protection for personnel in and around the vicinity of welding and cutting operations (other than the welder). NOTE These goggles should not be used in actual welding operations. 5-25. ELECTRODES AND THEIR USE a. General. When molten metal is exposed to air, it absorbs oxygen and nitrogen, and becomes brittle or is otherwise adversely affected. A slag cover is needed to protect molten or solidifying weld metal from the atmosphere. This cover can be obtained from the electrode coating, which protects the metal from damage, stabilizes the arc, and improves the weld in the ways described below. b. Types of Electrodes. The metal-arc electrodes may be grouped and classified as bare electrodes, light coated electrodes, and shielding arc or heavy coated electrodes. The type used depends on the specific properties required in the weld deposited. These include corrosion resistance, ductility, high tensile strength, the type of base metal to be welded; the position of the weld (i. e., flat, horizontal, vertical, or overhead); and the type of current and polarity required. c. Classification of Electrodes. The American Welding Society’s classification number series has been adopted by the welding industry. The electrode identification system for steel arc welding is set up as follows: (1) E indicates electrode for arc welding. (2) The first two (or three) digits indicate tensile strength (the resistance of the material to forces trying to pull it apart) in thousands of pounds per square inch of the deposited metal. (3) The third (or fourth) digit indicates the position of the weld. 0 indicates the classification is not used; 1 is for all positions; 2 is for flat and horizontal positions only; 3 is for flat position only. (4) The fourth (or fifth) digit indicates the type of electrode coating and the type of power supply used; alternating or direct current, straight or reverse polarity. (5) The types of coating, welding current, and polarity position designated by the fourth (or fifth) identifying digit of the electrode classification are as listed in table 5-4.

(6) The number E6010 indicates an arc welding electrode with a minimum stress relieved tensile strength of 60,000 psi; is used in all positions; and reverse polarity direct current is required. (3) The electrode identification system for stainless steel arc welding is set up as follows: (a) E indicates electrode for arc welding. (b) The first three digits indicated the American Iron and Steel type of stainless steel. (c) The last two digits indicate the current and position used. (d) The number E-308-16 by this system indicates stainless steel Institute type 308; used in all positions; with alternating or reverse polarity direct current. d. Bare Electrodes. Bare electrodes are made of wire compositions required for specific applications. These electrodes have no coatings other than those required in wire drawing. These wire drawing coatings have some slight stabilizing effect on the arc but are otherwise of no consequence. Bare electrodes are used for welding manganese steel and other purposes where a coated electrode is not required or is undesirable. A diagram of the transfer of metal across the arc of a bare electrode is shown in figure 5-29.

e. Light Coated Electrodes. (1) Light coated electrodes have a definite composition. A light coating has been applied on the surface by washing, dipping, brushing, spraying, tumbling, or wiping to improve the stability and characteristics of the arc stream. They are listed under the E45 series in the electrode identification system. (2) The coating generally serves the following functions: (a) It dissolves or reduces impurities such as oxides, sulfur, and phosphorus. (b) It changes the surface tension of the molten metal so that the globules of metal leaving the end of the electrode are smaller and more frequent, making the flow of molten metal more uniform. (c) It increases the arc stability by introducing materials readily ionized (i. e., changed into small particles with an electric charge) into the arc stream. (3) Some of the light coatings may produce a slag, but it is quite thin and does not act in the same manner as the shielded arc electrode type slag. The arc action obtained with light coated electrodes is shown in figure 5-30.

f. Shielded Arc or Heavy Coated Electrodes. Shielded arc or heavy coated electrodes have a definite composition on which a coating has been applied by dipping or extrusion. The electrodes are manufactured in three general types: those with cellulose coatings; those with mineral coatings; and those with coatings of combinations of mineral and cellulose. The cellulose coatings are composed of soluble cotton or other forms of cellulose with small amounts of potassium, sodium, or titanium, and in some cases added minerals. The mineral coatings consist of sodium silicate, metallic oxides, clay, and other inorganic substances or combinations thereof. Cellulose coated electrodes protect the molten metal with a gaseous zone around the arc as well as slag deposit over the weld zone. The mineral coated electrode forms a slag deposit only. The shielded arc or heavy coated electrodes are used for welding steels, cast iron, and hard surfacing. The arc action obtained with the shielded arc or heavy coated electrode is shown in figure 5-31.

g. Functions of Shielded Arc or Heavy Coated Electrodes. (1) These electrodes produce a reducing gas shield around the arc which prevents atmospheric oxygen or nitrogen from contaminating the weld metal. The oxygen would readily combine with the molten metal, removing alloying elements and causing porosity. The nitrogen would cause brittleness, low ductility, and in some cases, low strength and poor resistance to corrosion. (2) The electrodes reduce impurities such as oxides, sulfur, and phosphorus so that these impurities will not impair the weld deposit. (3) They provide substances to the arc which increase its stability and eliminate wide fluctuations in the voltage so that the arc can be maintained without excessive spattering. (4) By reducing the attractive force between the molten metal and the end of the electrode, or by reducing the surface tension of the molten metal, the vaporized and melted coating causes the molten metal at the end of the electrode to break up into fine, small particles. (5) The coatings contain silicates which will form a slag over the molten weld and base metal. Since the slag solidifies at a relatively slow rate, it holds the heat and allows the underlying metal to cool and slowly solidify. This slow solidification of the metal eliminates the entrapment of gases within the weld and permits solid impurities to float to the surface. Slow cooling also has an annealing effect on the weld deposit. (6) The physical characteristics of the weld deposit are modified by incorporating alloying materials in the electrode coating. The fluxing action of the slag will also produce weld metal of better quality and permit welding at higher speeds.

(b) Yellow -.5 percent zirconium. This type of electrode has a relatively low current-carrying capacity and a low resistance to contamination. Electrodes exposed to damp air for more than two or three hours should be dried by heating in a suitable oven (fig.pure tungsten. 5-32) for two hours at 500°F (260°C). (8) The coating produces a cup. cone.3 to 0. Moisture destroys the desirable characteristics of the coating and may cause excessive spattering and lead to the formation of cracks in the welded area. Storing Electrodes. concentrates and directs the arc. Tungsten Electrodes. and tungsten containing 0. 5 percent tungsten) electrodes are generally used on less critical welding operations than the tungstens which are alloyed. they should be stored in a moisture proof container. Electrodes should not be used if the core wire is exposed.3 to 0. tungsten containing 1 or 2 percent thorium.
i.5 percent zirconium. h. (c) Red -.1 percent thorium. or sheath (fig. reduces heat losses and increases the temperature at the end of the electrode. (3) Pure tungsten (99. (d) Brown -. (1) Nonconsumable electrodes for gas tungsten-arc (TIG) welding are of three types: pure tungsten.(7) The coating insulates the sides of the electrode so that the arc is concentrated into a confined area. Electrodes must be kept dry. 5-31) at the tip of the electrode which acts as a shield. (a) Green -. Bending the electrode can cause the coating to break loose from the core wire. (2) Tungsten electrodes can be identified as to type by painted end marks as follows.
.2 percent thorium.0. After they have dried. This facilitates welding in a deep U or V groove.

2 mm) might be used for butt joints in light gage material. 5-33). electron flow is from electrode to workpiece.
(7) The electrode extension beyond the gas cup is determined by the type of joint being welded.4 to 12. and greater resistance to contamination. Tungsten electrodes alloyed with thorium and zirconium retain their shape longer when touch-starting is used. This will prevent contamination of the electrode. The tungsten electrode of torch should be inclined slightly and the filler metal added carefully to avoid contact with the tungsten.5 percent zirconium generally fall between pure tungsten electrodes and thoriated tungsten electrodes in terms of performance. an extension beyond the gas cup of 1/8 in. high current-carrying capacity. while an extension of approximately 1/4 to 1/2 in. 5-34). (1) For dcsp. (6. There is. (6) Finer arc control can be obtained if the tungsten alloyed electrode is ground to a point (fig. Tungsten electrode points are difficult to maintain if standard direct current equipment is used as a power source and touch-starting of the arc is standard practice.3 to 0. longer life. (5) Tungsten electrodes containing 0. they must be operated at maximum current density to obtain reasonable arc stability. better arc-starting and arc stability. Maintenance of electrode shape and the reduction of tungsten inclusions in the weld can best be accomplished by superimposing a highfrequency current on the regular welding current.7 mm) might be necessary on some fillet welds. reground.(4) Thoriated tungsten electrodes (1 or 2 percent thorium) are superior to pure tungsten electrodes because of their higher electron output. electron flow is from workpiece to electrode. For example. j. If contamination does occur. the welding machine connections are electrode negative and workpiece positive (fig. some indication of better performance in certain types of welding using ac power. the welding current circuit may be hooked up as either straight polarity (dcsp) or reverse polarity (dcrp). Direct Current Welding. The polarity recommended for use with a specific type of electrode is established by the manufacturer. When electrodes are not grounded. and replaced in the torch. however. the welding machine connections are electrode positive and workpiece negative. the electrode must be removed. (3.
. In direct current welding. For dcrp.

the composition of the coating and the gases it produces may alter the heat conditions. 535). while another type of coating on the same electrode may provide a more desirable heat balance with reverse polarity. a 1/4-in.(2) For both current polarities. deep weld. If the polarity were reversed. The workpiece is dcsp and the electrode is dcrp. relatively shallow weld (fig. a 1/16-in. This will produce greater heat on the negative side of the arc. (1. dcrp requires a larger diameter electrode than does dcsp. for any given welding current.6-mm) diameter pure tungsten electrode can handle 125 amperes of welding current under straight polarity conditions.
.4-mm) diameter pure tungsten electrode is required to handle 125 amperes dcrp satisfactorily and safely. DCSP welding will produce a wide. but also the shape of the weld obtained. however. because of the larger electrode diameter and lower currents generally employed. However. this amount of current would melt off the electrode and contaminate the weld metal. when heavy coated electrodes are used. DCRP welding. One type of coating may provide the most desirable heat balance with straight polarity. (6. For example. Thus. Hence. (3) The different heating effects influence not only the welding action. gives a narrow. the greatest part of the heating effect occurs at the positive side of the arc.

which tends to break up the surface oxides. is a combination of dcsp and dcrp welding. the other half is dcrp. This can be best explained by showing the three current waves visually. bare. k. straight polarity is used with all mild steel. As shown in figure 5-36. (1) Alternating current welding. and the welding bead will be difficult to control. Reverse polarity is used in the welding of non-ferrous metals such as aluminum. (6) The proper polarity for a given electrode can be recognized by the sharp. (5) In general.(4) One other effect of dcrp welding is the so-called plate cleaning effect. or light coated electrodes. half of each complete alternating current (ac) cycle is dcsp. This surface cleaning action is caused either by the electrons leaving the plate or by the impact of the gas ions striking the plate. Alternating Current Welding. theoretically. monel. The wrong polarity will cause the arc to emit a hissing sound. cracking sound of the arc. and nickel. bronze. Reverse polarity is also used with sane types of electrodes for making vertical and overhead welds. and dirt usually present.
.

This is called rectification. low-power current. high-frequency. (e) The use of wider current range for a specific diameter electrode is possible.
. This high-frequency current jumps the gap between the electrode and the workpiece and pierces the oxide film. oxides.
(3) To prevent rectification from occurring. thereby forming a path for the welding current to follow. (b) Better arc stability is obtained. etc. For example. in no current at all flowed in the reverse polarity direction. scale. Direct Current Arc Welding Electrodes. Superimposing this high-voltage. to prevent the flow of current in the reverse polarity direction. on the surface of the plate tend. This is particularly useful in surfacing and hardfacing operations. high-frequency current on the welding current gives the following advantages: (a) The arc may be started without touching the electrode to the workpiece. (d) Welding electrodes have longer life.
l. it is common practice to introduce into the welding current an additional high-voltage. the current wave would be similar to figure 5-37.(2) Moisture. together with both dcsp and dcrp welds for comparison. (c) A longer arc is possible. (4) A typical weld contour produced with high-frequency stabilized ac is shown in figure 5-38. partially or completely..

Manganese promotes the formation of sound welds.(1) The manufacturer’s recommendations should be followed when a specific type of electrode is being used.. e. direct current shielded arc electrodes are designed either for reverse polarity (electrode positive) or for straight polarity (electrode negative). Recommendations from the manufacturer also include the type of base metal for which given electrodes are suited. brittleness. Sulfur acts as a slag. and stabilize the arc.
. and lack of fusion in the weld. and "cold shortness" (i. (2) Aluminum or aluminum oxide (even when present in 0. the arc stability will be affected. calcium oxide. straight polarity electrodes will provide less penetration than reverse polarity electrodes. nonferrous.. Direct current is preferred for many types of covered. and causes "hot shortness" (i. e. Iron oxide. Sulfur is particularly harmful to bare. (2) Alternating current is used in atomic hydrogen welding and in those carbon arc processes that require the use of two carbon electrodes. brittle when above red heat). It permits a uniform rate of welding and electrode consumption.01 percent). because the electrode will be consumed at a lower rate. low-carbon steel electrodes with a low manganese content. Alternating current is more desirable while welding in restricted areas or when using the high currents required for thick sections because it reduces arc blow. Thin or heavy coatings on the electrodes will riot completely remove the effects of defective wire. but not all. of the direct current electrodes can be used with alternating current. and other specific conditions. brittle when below red heat) in the weld. Alternating Current Arc Welding Electrodes. slag inclusions. n. they will impair the weld metal because they are transferred from the electrode to the molten metal with very little loss. silicon dioxide. (1) Coated electrodes which can be used with either direct or alternating current are available. Phosphorus causes grain growth. manganese oxide. Arc blow causes blowholes. (3) When phosphorus or sulfur are present in the electrode in excess of 0. Good penetration can be obtained from either type with proper welding conditions and arc manipulation. corrections for poor fit-ups. silicon. (1) If certain elements or oxides are present in electrode coatings. the composition and uniformity of the wire is an important factor in the control of arc stability. or both. In bare electrodes. m. Electrode Defects and Their Effects. In general. and for this reason will permit greater welding speed. breaks up the soundness of the weld metal. Many.04 percent. These defects increase in magnitude as the carbon content of the steel increases. direct current straight polarity is recommended. (2) In most cases. In carbon-arc processes where one carbon electrode is used. and iron sulphate unstable. bare and alloy steel electrodes.

the welding operator positions the work between the electrodes and pushes a switch to initiate the weld. including the electrodes which conduct the welding current to the work. Resistance welds are made with either semiautomatic or mechanized machines. Resistance welding machines are classified according to their electrical operation into two basic groups: direct energy and stored energy. is not uniform. Heat is generated by the passage of electrical current through a resistance current. c. The selection of resistance welding equipment is usually determined by the joint design. (3) The control equipment (timing devices) to initiate the time and duration of the current flow. parts are automatically fed into a machine. With the semiautomatic machine. Resistance welding is a group of welding processes in which the joining of metals is produced by the heat obtained from resistance of the work to the electric current. General. A resistance welding machine has three principal elements: (1) An electrical circuit with a welding transformer and a current regulator. resistance percussion welding. RESISTANCE WELDING a. and a secondary circuit. There are seven major resistance welding processes: resistance projection welding. The three factors involved in making a resistance weld are the amount of current that passes through the work. the pressure that the electrodes transfer to the work. production schedules. with the maximum heat being generated at the surfaces being joined.
Section IV. This equipment may also control the current magnitude. as well as the sequence and the time of other parts of the welding cycle. in a circuit of which the work is a part. resistance upset welding. then welded and ejected without welding operator assistance. The amount of current employed and the time period are related to the heat input required to overcome heat losses and raise the temperature of the metal to the welding temperature. resistance seam welding. and resistance high frequency welding. and economic considerations. Pressure is required throughout the welding cycle to assure a continuous electrical circuit through the work. Principal Elements of Resistance Welding Machines. b. Electrical Operation. and by the application of pressure. the weld programmer completes the sequence.
. resistance flash welding. construction materials. Standard resistance welding machines are capable of welding a variety of alloys and component sizes. In a mechanized setup. given the wire core of an electrode. and the time the current flows through the work. the electrode will produce welds inferior to those produced with an electrode of the same composition that has been properly heat treated.(4) If the heat treatment. RESISTANCE WELDING EQUIPMENT
5-26. quality requirements. resistance spot welding. (2) A mechanical system consisting of a machine frame and associated mechanisms to hold the work and apply the welding force.

is shown in figure 5-39. with its essential operating elements for manual operation. portable. These machines consist essentially of a cylindrical arm or extension of an arm which transmits the electrode force and in most cases.
(a) Rocker arm type. the electrode jaws are extended in such a manner as to permit a weld to be made at a considerable distance from the edge of the base metal sheet. Spot Welding. The electrodes are composed of a copper alloy and are assembled in a manner by which considerable force or squeeze may be applied to the metal during the welding process. (1) There are several types of spot welding machines.Machines in both groups may be designed to operate on either single-phase or three-phase power. press. A typical spot welding machine. the welding current. They are readily adaptable for spot welding of most weldable metals. The electrodes must be positioned so that both are in the plane of the
. including rocker arm. In these machines. The travel path of the upper electrode is in an arc about the fulcrum of the upper arm. d. and multiple type.

low-inertia heads. holders. A typical portable welding gun consists of a frame. hand grips. (c) Portable type. The same basic welding gun is used for the designs. solid. or both. in some cases. an electrical contactor and sequence timer. They may be designed for spot welding. (c) Rapid follow up of the electrode force by employing anti-friction bearings and lightweight. (d) Multiple spot welding type. and a cable and hose unit to carry power and cooling water between the transformer and welding gun. the moveable welding head travels in a straight line in guide bearings or ways. In this type of machine. (b) Precise electronic control of current and length of time it is applied. However. (d) High structural rigidity of the welding machine arms. an air or hydraulic actuating cylinder. (2) When spot welding aluminum.
. They utilize a number of transformers. the best results are obtained only if certain refinements are incorporated into these machines. and an initiating switch. and platens in order to minimize deflection under the high electrode forces used for aluminum. (b) Press type. These features include the following: (a) Ability to handle high current for short welding times. These are special-purpose machines designed to weld a specific assembly. the lower electrode is made of a piece of solid copper alloy with one or more electrode alloy inserts that contact the part to be welded. but it is mounted on a special "C" frame similar to that for a portable spot welding gun. A typical portable spot welding machine consists of four basic units: a portable welding gun or tool. a variable or dual force cycle to permit forging the weld nugget. For most applications. Press type machines are classified according to their use and method of force application. projection welding.horn axes. lower electrode. or manually with small bench units. Because of the radial motion of the upper electrode. a welding transformer and. Force is applied directly to the electrode through a holder by an air or hydraulic cylinder. conventional spot welding machines used to weld sheet metal may be used. or where variations in parts will not permit consistent contact with a large. Force may be applied by air or hydraulic cylinders. and to reduce magnetic deflections. a rectifier. The entire assembly can move as electrode force is applied to the weld location. The design of the gun is tailored to the needs of the assembly to be welded. Equalizing guns are often used where standard electrodes are needed on both sides of the weld to obtain good heat balance. these machines are not recommended for projection welding.

the lower electrode mounting and drive mechanism. Projection Welding. Seam welding machine controls must provide an on-off sequencing of weld current and a control of wheel rotation. or bar of small cross section and to join the seam continuously in pipe or tubing. Flash weld-fig is generally preferred for joining components of equal cross section end-to-end. g. a welding head consisting of an air cylinder. rod. electronic controls and contactor. Refrigerated cooling is often helpful.(e) Slope control to permit a gradual buildup and tapering off of the welding current. The press type resistance welding machine is normally used for projection welding. 5-40). Portable seam welding machines use this principle. The projection welding dies or electrodes have flat surfaces with larger contacting areas than spot welding electrodes. Seam Welding. Flash and upset welding machines are similar in construct ion. A seam welding machine is similar in principle to a spot welding machine. a ram. the secondary circuit connections. The major difference is the motion of the movable platen during welding and the mechanisms used to impart the motion. The components of a standard seam welding machine include a main frame that houses the welding transformer and tap switch. and wheel electrodes. the type used depending on the service requirements. the electrode is stationary and the work is moved. Flat nose or special electrodes are used. e. Flash welding machines are generally of much larger capacity than upset welding machines. Upset and Flash Welding. In some machines. In the traveling fixture type seam welding machine. the work is held in a fixed position and a wheel type electrode is passed over it. However. Several types of machines are used for seam welding. if used. (g) Good cooling of the Class I electrodes to prevent tip pickup or sticking.
f. and an upper electrode mounting and drive mechanism. except that wheel-shaped electrodes are used rather than the electrode tips used in spot welding. (f) Postheat current to allow slower cooling of the weld. both of these
. Upset welding is normally used to weld wire. The effectiveness of this type of welding depends on the uniformity of the projections or embossments on the base metal with which the electrodes are in contact (fig.

The hole through the thimble is plugged with a tapping pin. and tooling. Electrodes that hold the parts and conduct the welding current to them are mounted on the platens. THERMIT WELDING EQUIPMENT
5-27. Percussion Welding. movable platen. into which a magnesite stone thimble is fitted. metal is removed from the joint to permit a free flow of the thermit metal into the joint. The process is similar to flash and upset welding. At the bottom of the crucible. This thimble provides a passage through which the molten steel is discharged into the mold. electrodes to hold the parts and conduct the welding current.processes can be performed on the same type of machine. This process uses heat from an arc produced by a rapid discharge of electrical energy to join metals. electrical controls. (1) A standard flash welding machine consists of a main frame. In preparing the joint for thermit welding. A wax pattern is then made around the joint in the size and shape of the intended weld. Molten steel is produced by the thermit reaction in a magnesite-lined crucible. and a flashing and upsetting mechanism. This process joins metals with the heat generated from the resistance of the work pieces to a high frequency alternating current in the 10.000 hertz range. If necessary. High Frequency Welding. The crucible is charged by placing the correct quantity of thoroughly mixed thermit material in it. clamping mechanisms and fixtures. A mold made of refractory sand is built around the wax pattern and joint to hold the molten metal after it is poured. General. The sand mold is then heated to melt out the wax and dry the mold. stationary platen. The metals that are to be joined serve as electrodes. The process is entirely automatic and utilizes equipment designed specifically for this process. alined. a magnesite stone is burned.
Section V. a tap switch. Pressure is applied progressively during or immediately following the electrical discharge. and means to upset the joint. The mold should be properly vented to permit the escape of gases and to allow the proper distribution of the thermit metal at the joint. Thermit material is a mechanical mixture of metallic aluminum and processed iron oxide. A unit generally consists of a modified press-type resistance welding machine with specially designed transform. THERMIT WELDING (TW) a. and held firmly in place. i.000 to 500. and the rapid application of an upsetting force after heating is completed. A thermit welding crucible and mold is shown in figure 5-41. Two types of welding machines are used in percussion welding: magnetic and capacitor discharge. controls. the parts to be welded must be cleaned. h. which is covered with a fireresistant washer and refractory sand.
. A primary contactor is used to control the welding current. (2) Upset welding machines consist of a main frame that houses a transform and tap switch. a transformer.

which may be either portable or stationary. The valve handle is also used to free the valve from ashes. or it may be equipped
. and ash gate. blast valve. as shown in figure 5-42. It is made of cast iron and consists of a fire pot. The air blast passes through the base and is admitted to the fire through the valve. The essential parts of a forge are a hearth. The tuyere is a valve mechanism designed to direct an air blast into the fire. is the most important component of forge welding equipment.Section VI. The forge. The two types used in hand forge welding are described below. base with air inlet. One type of portable forge is shown in figure 5-42. The valve can be set in three different positions to regulate the size and direction of the blast according to the fire required. and a blower. a water tank. Portable Forge. a. a tuyere. and then applying pressure. FORGE WELDING TOOLS AND EQUIPMENT 5-28. A portable forge may have a handcrank blower. FORGES Forge welding is a form of hot pressure welding which joins metals by heating them in an air forge or other furnace.

The air blast valve usually has three slots at the top. the positions of which can be controlled by turning the valve. A hood is provided on the forge for carrying away smoke and fumes. In the updraft type. the smoke and fumes are drawn down under an adjustable hood and carried through a duct by an exhaust fan that is entirely separate from the blower. are available in both updraft and downdraft types. because the removal of furies and smoke is positive. The stationary forges. the smoke and gases pass up through the hood and chimney by natural draft or are drawn off by an exhaust fan. The stationary forge is similar to the portable forge except that it is usually larger with larger air and exhaust connections.
b. 5-43) is usually made of two forgings or steel castings welded together at the waist.
. The table or cutting block is soft so that cutters and chisels caning in contact with it will not be dulled. Anvil. (1) The anvil (fig. In the downdraft type. It cannot be easily damaged by hammering. The forge may have an individual blower or there may be a large capacity blower for a group of forges. 5-29. The opening of these slots can be varied to regulate the volume of the blast and the size of the fire.with an electric blower. The downdraft forge permits better air circulation and shop ventilation. FORGING TOOLS a. tempered tool steel which is welded to the top of the anvil. The face is made of hardened. like portable forges. The blower produces air blast pressure of about 2 oz per sq in. Stationary Forge.

flatters. 150 weighs 150 lb).
. b. and a vise are used in forging operations. punches. swages. (102 mm) back from the table to provide edges where stock can be bent without danger of cutting it. The hardy hole is square and is designed to hold the hardy. The height of the anvil should be adjusted so that the operator’s knuckles will just touch its face when he stands erect with his arms hanging naturally. and range in size from No 100 to No. Other Tools. (3) Anvils are designated by weight (i. fullers. No. In addition to the anvil. other tools such as hammers.(2) The edges of an anvil are rounded for about 4.00 in. bottom. and other special tools. chisels. The pritchel hole is round and permits slugs of metal to pass through when holes are punched in the stock. 300.e. tongs. All other edges are sharp and will cut stock when it is hammered against them. sledges.. although steel pedestals or bolsters are sometimes used. The anvil is usually mounted on a heavy block of wood. swage blocks. fullers.

Common methods of welding used in modern metal fabrication and repair are shown in figure 6-1.
. Various methods and materials may be used to accomplish good welding practices. Welding processes may be broken down into many categories. DESCRIPTION
6-1.CHAPTER 6 WELDING TECHNIQUES
Section I. GENERAL The purpose of this chapter is to outline the various techniques used in welding processes.

.

The formation of a joint between metals being arc welded may or may not require the use of pressure or filler metal. however. and may produce a slag covering as well. if needed. and difficulty in controlling the arc. or similar part. is basically the same as that used for stud welding.6-2. except that an inert gas or flux. The molten surfaces to be joined. and aluminum. is used for shielding. the arc is drawn between a bare or lightly coated consumable electrode and the workpiece. The arc is struck between the workpiece and an electrode that is mechanically or manually moved along the joint. In arc welding processes. but also melts and supplies filler metal to the joint. The electrode will be either a consumable wire rod or a nonconsumable carbon or tungsten rod which carries the current and sustains the electric arc between its tip and the workpiece. is produced by the extreme heat of an electric arc drawn between an electrode and the workpiece. and neither shielding nor pressure is used. or weld. The stud welding process produces a joining of metals by heating them with an arc drawn between a metal stud. or that remains stationary while the workpiece is roved underneath it. a separate rod or wire can supply filler material. and the workpiece. brittleness. ARC WELDING The term arc welding applies to a large and varied group of processes that use an electric arc as the source of heat to melt and join metals. Figure 6-2 shows a typical equipment setup for arc stud welding. because of its low strength. A consumable electrode is specially prepared so that it not only conducts the current and sustains the arc. the joining of metals. No shielding gas is used. are forced together under pressure. (1) Stud welding. Shielding gases and fluxes are used when welding
. a variation of stud welding. when properly heated. Metal Electrodes. such as argon or helium. Filler metal is obtained from the electrode.
(2) Gas shielded stud welding. When a nonconsumable electrode is used. a. The most common materials welded with the arc stud weld process are low carbon steel. or between two electrodes. This type of welding electrode is rarely used. This process. stainless steel. In bare metal-arc welding.

Basically. This granular material is called a flux.nonferrous metals such as aluminum and magnesium. It is responsible for the high deposition rates and weld quality that characterize the submerged arc welding process in joining and surfacing applications. The electrode is advanced in the direction of welding and mechanically fed into the arc. Pressure is not used and filler metal is obtained from the electrode or from a supplementary welding rod. electrode. The melted base metal and filler metal flow together to form a molten pool in the joint. Figure 6-3 shows a typical setup for gas shielded arc stud welding. The arc is shielded by a blanket of granular fusible material and the workpiece. the end of a continuous bare wire electrode is inserted into a mound of flux that covers the area or joint to be welded.
(3) Submerged arc welding. although it performs several other important functions. At the same time. the melted flux floats to the surface to form a protective slag cover. An arc is initiated. Submerged arc welding is distinguished from other arc welding processes by the granular material that covers the welding area. in submerged arc welding.
. causing the base metal. while flux is steadily added. Figure 6-4 shows the submerged arc welding process. This process joins metals by heating them with an arc maintained between a bare metal electrode and the workpiece. and flux in the immediate vicinity to melt.

(4) Gas tungsten-arc welding (TIG welding or GTAW). The arc is drawn between a nonconsumable tungsten electrode and the workpiece. A variety of tungsten electrodes are used with the process. arc. The shield gas protects the electrode and weld pool and provides the required arc characteristics. The operation of typical gas shielded arc welding machines may be found in TM 5-3431-211-15 and TM 5-3431-31315.
. if used. and the welding rod (wire) as it is being fed into the arc and weld pool. Figure 6-5 shows the relative position of the torch. gas shield. The electrode is normally ground to a point or truncated cone configuration to minimize arc wandering. Shielding is obtained from an inert gas or gas mixture. Pressure and/or filler metal may or may not be used. The arc fuses the metal being welded as well as filler metal. tungsten electrode.

gas mixture. The electrode covering is a source of arc stabilizers. Shielding is obtained from the decomposition of the electrode covering. and welding conditions.13 to 0. cast iron. The arc is drawn between a covered consumable metal electrode and workpiece. stainless steel. (0. electrode.06 in.
(6) Shielded metal-arc welding. aluminum. Electrodes used for MIG welding are quite small in diameter compared to those used in other types of welding. All commercially important metals such as carbon steel. Electrodes must always be provided as long. In this process. aluminum. stainless steels. Wire diameters 0. Pressure is not used and filler metal is obtained from the electrode. Figure 6-6 shows the gas metal arc welding process. and slags to support and protect the weld. electrode tip and molten weld metal are shielded from the atmosphere by a gas.15 cm) are average.(5) Gas metal-arc Welding (MIG welding or GMAW). continuous strands of tempered wire that can be fed continuously through the welding equipment. they should be clean and free of contaminants which may cause weld defects such as porosity and cracking. Shielding is obtained entirely from an externally supplied inert gas. or a mixture o f a gas and a flux. Since the small electrodes have a high surface-to-volume ratio. Shielded metal arc welding electrodes are available to weld carbon and low alloy steels. the melting rates of the electrodes are very high. gases to exclude air. coalescence is produced by heating metals with an arc between a continuous filler metal (consumable) electrode and the workpiece. metals to alloy the weld.05 to 0. Because of the small sizes of the electrode and high currents used in MIG welding. The arc. and copper can be welded with this process in all positions by choosing the appropriate shielding gas.
. The electrode wire for MIG welding is continuously fed into the arc and deposited as weld metal.

molybdenum steels. and stainless steel. and their alloys. A weld is made in one spot by drawing the arc between the electrode and workpiece. A continuous weld is made along faying surfaces by drawing the arc between an electrode and workpiece. When the two carbon electrodes are brought together. (8) Arc spot welding. Two types of electrodes are used for carbon arc welding: The pure graphite electrode does not erode away as quickly as the carbon electrode. (1) Carbon-arc welding. Pressure and/or filler metal may or may not be used. such as chrome. Shielding is obtained from the hydrogen. Gas tungsten arc welding and gas metal arc welding are the processes most commonly used to make arc spot welds. The arc is maintained between two metal electrodes in an atmosphere of hydrogen. Although the process has limited industrial use today. The weld is made without preparing a hole in either member. or flux may or may not be used. However. shielding gas. the arc is struck and established between them. Figure 6-7 describes the shielded metal arc welding process. the arc is drawn between electrode and the workpiece. In this process. Its main application is tool and die repair welding and for the manufacture of steel alloy chain. nickel. (9) Arc seam welding. Filler metal. the arc is drawn between two carbon electrodes. An arc spot weld is a spot weld made by an arc welding process. shielding gas. but is more expensive and more fragile. Shielding and pressure are not used. Filler
. flux-cored arc welding and shielded metal arc welding using covered electrodes can be used for making arc spot welds. Carbon Electrode.copper. The angle of the electrodes provides an arc that forms in front of the apex angle and fans out as a soft source of concentrated heat or arc flame. Monel. No shielding is use. or flux may or may not be used. (2) Twin carbon-arc welding. atomic hydrogen welding is used to weld hard-to-weld metals. Pressure and/or filler metal may or may not be used. Filler metal. softer than a single carbon arc. Inconel. and nickel. In this variation on carbon-arc welding.
(7) Atomic hydrogen welding. b.

In this carbon-arc variation. The twin carbon-arc welding process can also be used for brazing. The flames can also supply a protective reducing atmosphere over the molten metal pool which is maintained during welding. Pressure and/or filler metal may or may not be used. to produce a flame having sufficient energy to melt the base metal. and natural gas are not suitable for welding ferrous materials because the heat output of the primary flame is too low for concentrated heat transfer. the arc is drawn between a carbon electrode and the workpiece. heat is obtained from the combustion of hydrogen with oxygen. This process is also a variation of carbon arc welding. Manual welding methods are generally used. No filler metal is used.metal may or may not be used. b. Shielding is obtained from the combustion of a solid material fed into the arc. No pressure is used. Pressure and/or filler metal may or may not be used.Acetylene was originally used as the fuel gas in oxyfuel gas welding. have also been used. a weld is made simultaneously over the entire area of abutting surfaces with gas flames obtained from the combustion of a fuel gas with oxygen and the application of pressure. or in rare cases. Oxy-Hydrogen Welding. In this process. (4) Shielded carbon-arc welding. but is extensively used for welding lead. with air. but has limited use in oxyfuel gas welding because of its colorless flare. This process is used primarily for welding low melting point metals such as lead. the term gas welding is used to describe any welding process that uses a fuel gas combined with oxygen. Also referred to as oxyfuel gas welding. a.
. The molten metal from the plate edges and the filler metal intermix in a common molten pool and join upon cooling to form one continuous piece. The fuel gas and oxygen are mixed in the proper proportions in a chamber. or from a blanket of flux on the arc. Hydrogen has a maximum flame temperature of 4820°F (2660°C). Pressure and/or filler metal may or may not be used. or both. butane. which makes adjustment of the hydrogen-oxygen ratio difficult. Acetylene is normally used as a fuel gas in pressure gas welding. The torch is designed to give the welder complete control of the welding flare. allowing the welder to regulate the melting of the base metal and the filler metal. or the flame atmosphere is too oxidizing. Shielding is obtained from an inert gas or gas mixture. The arc is drawn between a carbon electrode and the workpiece. Pressure Gas Welding. and filler metal may or may not be used. except shielding by inert gas or gas mixture is used. such as MAPP gas. Hydrocarbon fuel gases such as propane. 6-3. and small parts. Gas welding processes are outlined below. Pressure gas welding has limited uses because of its low flame temperature. but other gases. which is generally a part of the welding tip assembly. GAS WELDING Gas welding processes are a group of welding processes in which a weld is made by heating with a gas flame or flares. In this process. The flames must provide high localized energy to produce and sustain a molten pool. light gage sections. (3) Gas-carbon arc welding.

torches. Figure 6-8 illustrates a furnace
. Furnace brazing is used extensively where the parts to be brazed can be assembled with the filler metal preplaced near or in the joint. Gas Welding with MAPP Gas. Air-Acetylene Welding. the flame does not contact the workpiece. or oxygen. The neutral MAPP gas flame very deep blue 6-4. Standard acetylene gages. c. the torch may be equipped with a single tip. Pressure and/or filler metal may or may not be used. either single or multiple flame. intense blue flame of the neutral flame acetylene flame. A neutral MAPP gas flame has a primary cone about 1 1/2 to 2 times as long as the primary acetylene flame. Torch brazing is performed by heating the parts to be brazed with an oxyfuel gas torch or torches. For manual torch brazing. Depending upon the temperature and the amount of heat required. but below that of the base metal. a. heat is obtained from the combustion of acetylene with oxygen. heat is obtained from the combustion of acetylene with air.c. compressed air. b. The filler metal is distributed to the closely fitted surfaces of the joint by capillary action. In this process. e. In furnace brazing. In this process. Twin Carbon-Arc Brazing. wire. No pressure is used. A MAPP gas carburizing flame will look similar to a carburizing acetylene flame will look like the short. Brazing is a group of welding processes in which materials are joined by heating to a suitable temperature and by using a filler metal with a melting point above 840°F (449°C). Cleaning and fluxing are necessary. Oxy-Acetylene Welding. Torch Brazing (TB). the fuel gas may be burned with air. and filler metal may or may not be used. The various brazing processes are described below. This process is used extensively for soldering and brazing of copper pipe. a furnace produces the heat necessary for welding. In this process. This process produces the hottest flame and is currently the most widely used fuel for gas welding. d. an arc is maintained between two carbon electrodes to produce the heat necessary for welding. Furnace Brazing. In this process. Brazing filler metal may be preplaced at the joint or fed from handheld filler metal. brazing operation. or shim form. and welding tips usually work well with MAPP gas. Automated TB machines use preplaced fluxes and preplaced filler metal in paste. BRAZING.

In chemical bath dip brazing. The salt bath furnishes the heat necessary for brazing and usually provides the necessary protection from oxidation. For induction brazing. the workpiece acts as a short circuit in the flow of an induced high frequency electrical current. as shown in figure 6-10. Induction Brazing. Once heated in this manner. The heat is obtained from the resistance of the workpiece to the current. In molten metal bath dip brazing. The salt bath is contained in a metal or other suitable pot and heated. In this process. and vacuum tube oscillator.
e. brazing can begin. Three common sources of high frequency electric current used for induction brazing are the motor-generator. There are two methods of dip brazing: chemical bath and molten metal bath. the brazing fillermetal is preplaced and the assembly is immersed in a bath of molten salt. resonant spark gap. Dip Brazing. A cover of flux should be maintained over the molten bath to protect it from oxidation. the parts are immersed in a bath of molten brazing filler metal contained in a suitable pot. Careful design of the joint and the coil are required to assure the surfaces of all members of the joint reach the brazing temperature at the same time. Dip brazing is mainly
. the parts are placed in or near a water-cooled coil carrying alternating current.d. Typical coil designs are shown in figure 6-9.

In flow brazing.27 cm). brazed are supported in a position which enables radiant energy to be focused on the joint. Infrared Brazing (IRB). Infared brazing uses a high intensity quartz lamp as a heat source. The parts of the joint are a part of the electrical current. The ends of wires or parts must be held firmly together when removed from the bath until the brazing filler metal solidifies.50 in. Pressure should be maintained until the joint has solidified. heat is obtained from molten. (1. high-current transformer.used for joining small parts such as wires or narrow strips of metal.
. The assembly and the lamps can be placed in an evacuated or controlled atmosphere. The process is suited to the brazing of very thin materials and is normally not used on sheets thicker than 0. g. tungsten or steel. Flow Brazing. The heat necessary for resistance brazing is obtained from the resistance to the flow of an electric current through the electrodes and the joint to be brazed. molybdenum. In this process. Figure 6-11 illustrates the equipment used for infrared brazing. h. i. Brazing is done by the use f a low-voltage.
f. heat is obtained from heated blocks applied to the part to be joined. Resistance Brazing. The conductors or electrodes for this process are made of carbon. Block Brazing. nonferrous metal poured over the joint until the brazing temperature is obtained. The parts to be brazed are held between two electrodes and the proper pressure and current are applied.

but by the mechanism involved. A joint is formed by holding the brazement at a suitable temperature for a sufficient time to allow mutual diffusion of the base and filler metals. diffusion brazing is not defined by its heat source. by which the heat required to melt and flow a commercial filler metal is generated by a solid state exothermic chemical reaction. the DFB joint remelts at temperatures approaching that of the base metal. Special Processes. Also. The DFB process produces stronger joints than the normal brazed joint. The process uses the reaction heat in bringing adjoining or nearby metal interfaces to a temperature where preplaced brazing filler metal will melt and wet the metal interface surfaces.1 cm) thick. Although DFB requires a relatively long period of time (30 minutes to as long as 24 hours) to complete. it can produce many parts at the same time at a reasonable cost. Furnaces are most frequently used for this method of processing. An exothermic chemical reaction is any reaction between two or more reactants in which heat is given off due to the free energy of the system. (1) Blanket brazing is another process used for brazing. and no filler metal should be discernible in the finished microstructure. The brazing filler metal can be a commercially available one
. k. Many parts that are difficult to braze by other processes can be diffusion brazed. Diffusion Brazing (DFB).5 to 5. Both butt and lap joints having superior mechanical properties can be produced. Radiation is responsible for the majority of the heat transfer.j. and most of the heat is transferred to the parts by conduction and radiation. (2) Exothemic brazing is another special process. The joint produced has a composition considerably different than either the filler metal or base metal. Much heavier parts can also be brazed since thickness has very little bearing on the process. and the parts are usually fixtured mechanically or tack welded together. The typical thickness of the base metals that are diffusion brazed range from very thin foil up to 1 to 2 in. Exothermic brazing uses simple tooling and equipment. A blanket is resistance heated. (2. Unlike all of the previous brazing processes.

The only limitations may be the thickness of the metal that must be heated through and the effects of this heat. forming a weld. Such welds are leaktight. g. This weld is made simultaneously over the entire area of abutting surfaces by the heat obtained from an arc. with or without the application of an upsetting
. embossments. or progressively along a joint. A variation of this process is the roll spot weld. and the metal is heated above its melting point. the size and shape of the individually formed welds are limited primarily by the size and contour of the electrodes. Resistance Seam Welding. A force applied immediately following heating produces an expulsion of metal and the formation of a flash. force is applied before heating starts to bring the faying surfaces in contact. Upset Welding. heat is created at the joint by its resistance to the flow of the electric current. In both processes. or any previous heat treatment. Force is applied to upset the joint and start a weld when the metal reaches welding temperature. RESISTANCE WELDING Resistance welding consists of a group of processes in which the heat for welding is generated by the resistance to the electrical current flow through the parts being joined. d. Percussion Welding. High frequency welding includes those processes in which the joining of metals is produced by the heat generated from the electrical resistance of the workpiece to the flow of high-frequency current. In resistance spot welding. the weld is made either simultaneously over the entire area of two abutting surfaces. e. c. b. The electrodes apply pressure. in which the spot spacing is increased so that the spots do notoverlap and the weld is not leaktight. These welds are localized at points predetermined by the design of the parts to be welded. Projection Welding. a. A pair of electrodes conducts electrical current through the sheets. or intersections.having suitable melting and flow temperatures. It is extinguished by pressure applied percussively during the discharge. on the metal properties. Pressure is maintained throughout the heating period. In this process. The welding current is concentrated at the point of joining using cylindrical electrodes with spherical tips. The weld is made simultaneously over the entire area of abutting surfaces by the application of pressure after the heating is substantially completed. The electrodes apply pressure. Flash Welding. High–Frequency Welding. the electrodes apply pressure. Heat is also created by arcs at the interface. In some cases. The localization is usually accomplished by projections. In this process. f. It is commonly used to weld two overlapping sheets or plates which may have different thicknesses. using pressure. This weld is a series of overlapping spot welds made progressively along a joint by rotating the circular electrodes. Resistance Spot Welding. 6-5. The various resistance processes are outlined below. The arc is produced by a rapid discharge of electrical energy. Heat for welding is obtained from the resistance to the flow of electric current through the metal at the joint.

Normal heat losses cause the mass of molten metal to solidify. THERMIT WELDING a. Filler metal is obtained from the liquid metal. preheating is often eliminated. When the filler metal has cooled. Themit welding utilizes gravity. The heat for welding is obtained from an exothermic reaction or chemical change between iron oxide and aluminum.
. b. The exothermic reaction is relatively slow and requires 20 to 30 seconds. Almost all high-frequency welding techniques apply some force to bring the heated metals into close contact.force. melting occurs at the edges of the joint and alloys with the molten steel from the crucible. The superheated steel is contained in a crucible located immediately above the weld joint. machining. Information on thermit welding equipment may be found in Section V of Chapter 5. and the weld is completed. Once the reaction is started. The two processes that utilize high-frequency current to produce the heat for welding are high-frequency resistance welding and high-frequency induction welding. an upset or bulging of metal occurs in the weld area. The parts to be welded are aligned with a gap between them. or grinding. preheating within the mold cavity may be necessary to bring the pats to welding temperature and to dry out the mold. This reaction is shown by the following formula: 8A1 + 3fe304 = 9FE + 4A1203 + Heat The temperature resulting from this reaction is approximately 4500°F (2482°C). sometimes called induction resistance welding. which causes the molten metal to fill the cavity between the parts being welded. If the parts are small. During the application or force. The making of a thermit weld is shown in figure 6-12. The thermit welding process is applied only in the automatic mode. Thermit welding (TW) is a process which joins metals by heating them with superheated liquid metal from a chemical reaction between a metal oxide and aluminum or other reducing agent. all unwanted excess metal may be removed by oxygen cutting. coalescence occurs. The surface of the completed weld is usually sufficiently smooth and contoured so that it does not require additional metal finishing. It is very similar to the foundry practice of pouring a casting. with or without the application of pressure. If the parts to be welded are large. Since it is almost twice as hot as the melting temperature of the base metal. regardless of the amount of chemicals involved. c. The superheated steel runs into a mold which is built around the parts to be welded. 6-6. d. The difference is the extremely high temperature of the molten metal. it continues until completion.

If the cross-sectional area or thicknesses of the parts to be joined are quite large. Distortion is minimized since the weld is accomplished in one pass and since cooling is uniform across the entire weld cross section.e. as the metal cools. a solid homogenous weld results. g. and. This material also includes enough of the igniting material so that the exothermic reaction is started by means of a special lighter. the exothermic reaction is a reduction of copper oxide by aluminum. the parts to be joined must be extremely clean. When welding nonferrous materials. The high-temperature molten copper flows into the mold. Thermit welds can also be used for welding nonferrous materials. In welding copper and aluminum cables. Special kits are available that provide the molds for different sizes of cable and the premixed thermit material. The most popular uses of nonferrous thermit welding are the joining of copper and aluminum conductors for the electrical industry. There is normally shrinkage across the joint.
. NOMENCLATURE OF THE WELD
6-7. the molds are made of graphite and can be used over and over. which produces molten superheated copper.
Section II. Welds can be made with the parts to be joined in almost any position as long as the cavity has vertical sides. f. The deposited weld metal is homogenous and quality is relatively high. In these cases. the primary problem is to provide sufficient thermit metal to fill the cavity. h. The amount of thermit is calculated to provide sufficient metal to produce the weld. A flux is normally applied to the joint prior to welding. melts the ends of the parts to be welded. but little or no angular distortion. The amount of steel produced by the reaction is approximately one-half the original quantity of thermit material by weight and one-third by volume. GENERAL Common terms used to describe the various facets of the weld are explained in pargraphs 6-8 and 6-9 and are illustrated in figure 6-13.

. The fusion zone is the area of base metal melted as determined in the cross section of a weld. SECTIONS OF A WELD a.6-8. Fusion Zone (Filler Penetration).

MULTIPASS WELDS a. Toe of the Weld. (2) Unequal leg-length fillet welds. This is exposed surface of the weld. and the nomenclature applying to the grooves used in butt welding are shown in figure 6-14.
. The nomenclature of the weld. This is the junction between the face of the weld and the base metal. the zones affected by the welding heat when a butt weld is made by more than one pass or layer. The leg of a fillet weld is the distance from the root of the joint to the toe of the fillet weld. Figure 6-15 is based on weld type and position. Root of the Weld. 6-9. (1) Theoretical throat. The size of the weld is designated by the leg-length of the largest right triangle that can be inscribed within the fillet weld cross section.b. h. There are two legs in a fillet weld. Reinforcement of the Weld. Throat of a Fillet Weld. Face of the Weld. This is the point at which the bottom of the weld intersects the base metal surface. This is distance from the root of a fillet weld to the center of its face. (2) Actual throat. f. The size of the weld is designated by leg-length of the largest isosceles right triangle that can be scribed within the fillet weld cross section. This is the weld metal on the face of a groove weld in excess of the metal necessary for the specified weld size. g. d. This is the perpendicular distance of the weld and the hypotenuse of the largest right triangle that can be inscribed within the fillet weld cross section. (3) Groove weld. as shown in the cross section of weld. (1) Equal leg-length fillet welds. The size of the weld is the depth of chamfering plus the root penetration when specified. c. Size of the Weld. made by an arc or gas welding process on the side from which the welding was done. Leg of a Fillet Weld. e.

.

.

.

.

plate. A weld is a localized coalescence of metals or nonmetals produced either by heating the materials to a suitable temperate with or without the application of pressure. The weld metal in the first layer is also refined in structure by the welding heat of the second layer. The five basic types of joints are described below and shown in figure 6-16. or soldered joint. Welding is a materials joining process used in making welds.
. b. Base metal is the material to be welded. sheet. soldered. The edges should be prepared to permit fusion without excessive melting. forgings.
Section III. c.b. Preparation of the metal for welding depends upon the form. which can be made of many or few metal parts. The secondary heat zone is the area affected in the second pass and overlaps the primary heat zone. The portion of base metal that hardens or changes its properties as a result of the welding heat in the primary zone is partly annealed or softened by the welding heat in the secondary zone. TYPES OF WELDS AND WELDED JOINTS
6-10. there must be weld joints between the various pieces that make the weldment. To produce a usable structure or weldment. d. and other impurities must be removed from the joint edges or surfaces to prevent their inclusion in the weld metal. The two heating conditions are important in determining the order or sequence in depositing weld metal in a particular joint design. A properly prepared joint will keep both expansion on heating and contraction on cooling to a minimum. and is used in all of the welding process definitions. with or without the use of filler metal. oxides. the load the weld will be required to support. A weldment is an assembly of component parts joined by welding. These joint types or designs are also used by other skilled trades. brazed. rust. or cut. Coalescence is a growing together or a growing into one body. Care must be taken to keep heat loss due to radiation into the base metal from the weld to a minimum. All mill scale. The properties of a welded joint depend partly on the correct preparation of the edges being welded. and the pieces may be in the form of rolled shapes. There are five basic types of joints for bringing two members together for welding. Filler metal is the material to be added in making a welded. or by the application of pressure alone. and the available means for preparing the edges to be joined. A weldment may contain metals of different compositions. thickness. or castings. pipe. GENERAL a. The primary heat zone is the area fused or affected by heat in the first pass or application of weld metal. and kind of metal. The joint is the junction of members or the edges of members which are to be joined or have been joined.

(2) C. or carbon arc air cutting or gouging. (3) E. Plane square butt joints in light sections are shown in figure 6-17. not at the edge of one part. Corner joint .parts at approximately right angles. T joint .parts in approximately the same plane. machining. Butt joint .between overlapping parts. (5) T.
.an edge of two or more parallel parts. scales. dirt. These edges can be prepared by flame cutting. flame grooving. This type of joint is used to join the edges of two plates or surfaces located in approximately the same plane. (4) L.(1) B. 6-11. BUTT JOINT a. Lap joint .parts at approximately right angles and at the edge of both parts. Edge joint . chipping. Grooved butt joints for heavy sections with several types of edge preparation are shown in figure 6-18. The edge surfaces in each case must be free of oxides. or other foreign matter. grease. shearing.

6-12. half open. CORNER JOINT a. The common corner joints are classified as flush or closed. When the closed joint is used
. and full open. The edges of heavier sections (1/2 to 2 in. In making the joint by oxyacetylene welding. (0. tanks. box frames.91 cm) and up are prepared as shown in view D.27 to 5.
c.27 cm) can be welded using the single V or single U joints as shown in views A and C.95 to 1. figure 6-18. fig. This type of joint is used to join two members located at approximately right angles to each other in the form of an L. The fillet weld corner joint (view A. fig. and insure better weld metal qualities in heavy sections than joints prepared from one side only. figure 6-18. Plate thicknesses 3/8 to 1/2 in. and little or no filler metal is added. The edges of heavier sections should be prepared as shown in views B and D. (1. In arc welding. (1. In general. butt joints prepared from both sides permit easier welding. 6-18) is more satisfactory and requires less filler metal than the single V groove when welding heavy sections and when welding in deep grooves. 6-19) is used on light sheet metal. produce less distortion. only a very light bead is required to make the joint. Thickness of 3/4 in.08 cm)) are prepared as shown in view B. figure 6-18. usually 20 gage or less. b. the overlapping edge is melted down. 6-19) is used in the construction of boxes. figure 6-18. The double V groove joint requires approximately one-half the amount of filler metal used to produce the single V groove joint for the same plate thickness. The square butt joints shown in figure 6-16 are used for butt welding light sheet metal.b. fig. The closed corner joint (view B. The single U groove (view C. and on lighter sheets when high strength is not required at the joint. and similar fabrications.

The open corner joint (view C. This joint is used when welding can only be performed on one side and when loads will not be severe. EDGE JOINT This type of joint is used to join two or more parallel or nearly parallel members. Half open comer joints are suitable for material 12 gage and heavier. figure 6-20. f. figure 6-20. the lapped plate is V beveled or U grooved to permit penetration to root of the joint. Filler metal is used in this joint. etc.
b. tanks for liquids. It is not very strong and is used to join edges of sheet metal. An offset lap joint (view C. housing. On heavy plates. 6-21). Corner joints on heavy plates are welded from both sides as shown in view D. requires that the edges be beveled in order to secure good penetration and fusion of the side walls. The double lap joint is welded on both sides and develops the full strength of the welded members (view B. figure 6-21. d. The edges are fused together so no filler metal is required. sufficient filler metal is added to fuse or melt each plate edge completely and to reinforce the joint.for heavy sections. The two edges are melted down and filler metal is added to fill up the corner. then reinforced from the back side with a seal bead. No preparation is necessary other than to clean the edges and tack weld them in position. e. Light sheets are welded as shown in view B. 6-13. 6-21) is used where two overlapping plates must be joined and welded in
. 6-14. fig. The heavy plate joint as shown in view C. mufflers. Two parallel plates are joined together as shown in view A. edges of angles. fig. LAP JOINT This type of joint is used to join two overlapping members. figure 6-19. 6-19) is used on heavier sheets and plates. A single lap joint where welding must be done from one side is shown in view A. The joint is first welded from the outside. figure 6-20. This type of joint is the strongest of the corner joints. reinforcing plates in flanges of I beams. fig.

The single beveled joint (view B. 6-23) is used heavy plates that can be welded from both sides. 6-23) is used on heavy plates that can be welded from both sides.the same plane.
6-15. but the surface of one plate or section is not in the same plane as the end of the other surface. The included angle of bevel in the preparation of tee joints is approximately half that required for butt joints. This type of joint is stronger than the single lap type. fig. fig. figure 6-23. The double beveled joint (view C. which requires no preparation other than cleaning the end of the vertical plate and the surface of the horizontal plate.
b. Other edge preparations used in tee joints are shown in figure 6-23. Tee joints are used to weld two plates or section with surfaces located approximately 90 degrees to each others at the joint. fig. 6-23) is used for welding very heavy plates form both sides. is shown in view A. A plain tee joint. A plain tee joint welded from both sides is shown in view B. fig. TEE JOINT a. The single J joint (view D. The double J joint (view E. but is more difficult to prepare.
. 623) used for welding plates 1 in. figure 6-22. thick or heavier where welding is done from one side.

slot welds. There are many different types of welds. There are seven basic types of groove welds.c. The most popular weld is the fillet weld. or surface is prepared. Care must be taken to insure penetration into the root of the weld. which are best described by their shape when shown in cross section. and backing welds. surfacing welds. The type of weld used will determine the manner in which the seam. Joints are combined with welds to make weld joints. 6-16. General. Examples are shown in figure 6-26. seam welds. Each must be described to completely describe the weld joint. which are shown in figure 6-25. This penetration is promoted by root openings between the ends of the vertical members and the horizontal surfaces. The second most popular is the groove weld. Fillet welds are shown by figure 6-24.
. plug welds. It is important to distinguish between the joint and the weld. named after its cross-sectional shape. joint. TYPES OF WELDS a. Other types of welds include flange welds.

.

Groove Weld. See figure 6-27 for the standard types of groove welds.b.
. These are beads deposited in a groove between two members to be joined.

These are welds composed of one or more strings or weave beads deposited on an unbroken surface to obtain desired properties or dimensions.c. Surfacing weld (fig. This type of weld is used to build up surfaces or replace metal on worn surfaces. 6-28).
. It is also used with square butt joints.

. Such welds are often used in place of rivets. NOTE A fillet welded hole or a spot weld does not conform to this definition. 6-28). This is a weld of approximately triangular cross section joining two surfaces at approximately right angles to each other. Plug Weld (fig. fig. Slot Weld (fig. Flash Weld (fig. Plug welds are circular welds made through one member of a lap or tee joint joining that member to the other. 6-29). Fillet Weld (top. NOTE A fillet welded slot does not conform to this definition. 6-28). e. The weld may or may not be made through a hole in the first member. as in a lap or tee joint. This is a weld made in an elongated hole in one member of a lap or tee joint joining that member to the surface of the other member that is exposed through the hole.d. 6-28). This hole may be open at one end and may be partially or completely filled with weld metal. if a hole is used. A weld made by flash welding (para 6-5 d). the walls may or may not be parallel and the hole may be partially or completely filled with weld metal. g. f.

h. this term infers resistance seam welding. A weld made by arc spot or resistance spot welding (para 6-5 a). 6-29). this term infers a resistance spot weld. 6-29). j. 6-29). A weld made by upset welding (para 6-5 e). Seam Weld (fig. Where the welding process is not specified. i. Upset Weld (fig. Spot Weld (fig.
. A weld made by arc seam or resistance seam welding (para 6-5 b). Where the welding process is not specified.

All welding can be classified according to the position of the workpiece or the position of the welded joint on the plates or sections being welded. GENERAL Welding is often done on structures in the position in which they are found. There are four basic welding positions. Techniques have been developed to allow welding in any position. and surface welds may be made in all of the following positions. Some welding processes have all-position capabilities.Section IV. Pipe welding positions are shown in figure 6-32. Fillet. while others may be used in only one or two positions. groove. which are illustrated in figures 630 and 6-31. WELDING POSITIONS
6-17.
.

however. FLAT POSITION WELDING In this position. Flat welding is the preferred term. figure 6-31 for examples of flat position welding for fillet and groove welds). (See view A. figure 6-30 and view A.6-18. and the face of the weld is approximately horizontal. the same position is sometimes called downhand. the welding is performed from the upper side of the joint.
.

In this pipe welding position. Horizontal pipe rolled Weld (1) Align the joint and tack weld or hold in position with steel bridge clamps with the pipe mounted on suitable rollers (fig. b. View B. 6-20. figures 6-30 and 6-31. illustrates a horizontal fillet weld. Pipe welding positions are shown in figure 6-32. POSITIONS FOR PIPE WELDING Pipe welds are made under many different requirements and in different welding situations.6-19. In this pipe welding position. The welding position is dictated by the job. Pipe welding positions are shown in figure 6-32. Pipe welding positions are figure shown in figure 6-32. Positions and procedures for welding pipe are outlined below. View B. the axis of the pipe is approximately horizontal. b. In general. a. and the welding is performed in the horizontal position. a. the axis of the weld is approximately vertical. but in sane cases can be rolled for flat-position work. Horizontal Rolled Weld. HORIZONTAL POSITION WELDING NOTE The axis of a weld is a line through the length of the weld. In this position. the axis of the pipe is vertical. the position is fixed. 6-22. 6-33). and the pipe is not rotated during welding. the welding is performed from the underside of a joint. VERTICAL POSITION WELDING a. In this position. Vertical welding positions are shown in view C. In vertical position pipe welding. Fillet Weld. The pipe may or may not be rotated. figure 6-30. d. the axis of the weld lies in an approximately horizontal plane and the face of the weld lies in an approximately vertical plane. In this position. Start welding at point C. welding is performed in the flat position by rotating the pipe. 6-21. c. Overhead position welds are illustrated in view D. Horizontal Fixed Weld. figure 6-31.
. OVERHEAD POSITION WELDING In this welding position. Groove Weld. figures 6-30 and 6-31. figure 6-33. welding is performed on the upper side of an approximately horizontal surface and against an approximately vertical surface. illustrates a horizontal groove weld. perpendicular to the cross section at its center of gravity.

6-33) is similar to that for a vertical weld. After welding has been started. the pipe is set up so that the tack welds are oriented approximately as shown in figure 6-34. When the pipe is being rotated. rotate the pipe clockwise until the stopping point of the weld is at point C and again weld upward to point B. b. the pipe must not be moved in any direction. the torch should be held between points B and C and the pipe rotated past it. When point B is reached. This will insure a complete fusion of the advancing weld with the starting point. Horizontal Pipe Fixed Position Weld. As point B is approached.64 cm) in thickness. (3) The weld should be stopped just before the root of the starting point so that a small opening remains.
(2) The position of the torch at point A (fig. the weld assumes a nearly flat position and the angles of application of the torch and rod are altered slightly to compensate for this change. (0. (4) If the side wall of the pipe is more than 1/4 in. so that the area surrounding the junction point is at a uniform temperature. The starting point is then reheated. a multipass weld should be made. (1) After tack welding.progressing upward to point B.
.

fig. Step 2. Step 3. the pipe is welded in four steps as described below. the weld is made in two stages. then return to the top and work down the other side (2. Start at the top (fig.
. Step 1. the speed is approximately three times that of the upward welding method. weld upward to the 3 o’clock position. fig. Step 4. Starting back at the 3 o’clock position. With arc welding. weld upward to the top overlapping the bead. since the higher temperature of the electric arc makes possible the use of greater welding speeds.(2) When welding in the horizontal fixed position. Starting back at the bottom. 6-35) and work down one side (1. Starting at the bottom or 6 o'clock position. 6-35) to the bottom. The welding downward method is particularly effective with arc welding. Starting back at the 9 o’clock position. weld to the top. (3) When welding downward. weld upward to the 9 o'clock position. 6-35) to join with the previous weld at the bottom.

If a lineup clamp is used. As much root bead as the bars of the
. wherein the joint is horizontal.(4) Welding by the backhand method is used for joints in low carbon or low alloy steel piping that can be rolled or are in horizontal position. (1. Vertical Pipe Fixed Position Weld. Multipass Arc Welding.22 to 2. The weld is started at the tack and carried continuously around the pipe. If a backing ring is used. 6-37) is started at the bottom of the groove while the clamp is in position. When no backing ring is used. care should be taken to build up a slight bead on the inside of the pipe. One pass is used for wall thicknesses not exceeding 3/8 in.59 cm). 6-36). (1) Root beads. the root bead (view A.59 to 2. is most frequently welded by the backhand method (fig.95 to 1.22 cm). Pipe in this position. three passes for wall thicknesses 5/8 to 7/8 in. and four passes for wall thicknesses 7/8 to 1-1/8 in. fig.87 cm). (0. (0. (2.95 cm).
d. c. two passes for wall thicknesses 3/8 to 5/8 in. the root bead should be carefully fused to it.

(1. Travel angle is the angle that the electrode. Aluminum pipe welding.59 cm) wide and approximately 1/16 in. (0. makes with a reference line extending from the center of the pipe through the arc in the plane of the weld axis. or centerline of the welding gun.16 cm) above the outside surface of the pipe when complete. the work angle is the angle that the electrode. fig. or centerline of the welding gun. The travel angle is
. (3) Finish beads. makes with a reference line perpendicular to the axis of the weld in the plane of the weld axis. or centerline of the welding gun. Care should be taken that the filler beads (view B. special joint details have been developed and are normally associated with combination-type procedures. fig. A backing ring is not used in most cases. Figure 639 illustrates the travel angle for fillet and groove welds. Work angle is the angle that the electrode. 6-23. this is a weave bead about 5/8 in. e.lineup clamp will permit should be applied before the clamp is removed. The finish beads (view C. For pipe welding. or centerline of the welding gun.
(2) Filler beads. figure 6-37. Figure 6-38 shows the work angle for a fillet weld and a groove weld. It may be used for structural applications in which pipe and tubular members are used to transmit loads rather than materials. FOREHAND WELDING a. 6-37) are applied over the filler beads to complete the joint. Usually. in order to remove any undercut causal by the deposition of the root bead. makes with the referenced plane or surface of the pipe in a plane extending from the center of the pipe through the puddle. The rectangular backing ring is rarely used when fluids are transmitted through the piping system. the travel angle is the angle that the electrode. makes with the referenced plane or surface of the base metal in a plane perpendicular to the axis of a weld. One or more filler beads around the pipe usually will be required. For pipe welding. The finished weld is shown in view D. 6-37) are fused into the root bead. For aluminum pipe. Complete the bead after the clamp is removed.

the heat can be carefully balanced to melt the end of the rod and the side walls of the plate into a uniformly distributed molten puddle. The heat reflected backwards from the rod keeps the metal molten. The flame is pointed in the direction of welding and directed between the rod and the molten puddle. Figure 6–39 shows both drag angles and push angles. By moving the torch and the rod in opposite semicircular paths.
. is also known as forehand welding.further described as a drag angle or a push angle. in the direction of welding as shown in figure 6-40. The rod is dipped into the leading edge of the puddle so that enough filler metal is melted to produce an even weld joint. In forehand welding. the welding rod precedes the torch.
b. The torch is held at an approximately 30 degree angle from vertical. This position permits uniform preheating of the plate edges immediately ahead of the molten puddle. which points forward in the direction of travel. The metal is distributed evenly to both edges being welded by the motion of the tip and rod. The push angle.

Section V. In general. with the flame directed at the molten puddle. A 60 degree included angle of bevel is sufficient for a good weld. In this method. is illustrated in figure 6-41. also known as drag angle. The drag angle points backward from the direction of travel. Backhand welding. a relatively large molten puddle is required. The torch is held at an angle approximately 30 degrees from the vertical.
b. Some difficulties are encountered in welding heavier plates for the reasons given below: (1) In forehand welding. Backhand welding is used principally for welding heavy sections because it permits the use of narrower V's at the joint. (2) Because of this wide V. there is less puddling. 6-24. The welding rod is between the flame and the molten puddle. When metal cools. High-temperature heat is responsible for much of the welding warpages and stresses that occur. EXPANSION AND CONTRACTION IN WELDING OPERATIONS
6-25. This position requires less transverse motion than is used in forehand welding. c. and fusion of the weld metal to the base metal. the edges of the plate must be beveled to provide a wide V with a 90 degree included angle. BACKHAND WELDING a. good penetration. This method is satisfactory for welding sheets and light plates in all positions. and less welding rod is used with this method than with the forehand method. it contracts in all directions. the torch precedes the welding rod. When metal is heated. away from the direction of welding.
. Most of the welding processes involve heat.c. This edge preparation is necessary to insure satisfactory melting of the plate edges. it expands in all direction. It is difficult to obtain a good joint when the puddle is too large. GENERAL a. as shown in figure 6-41. Some distortions caused by weld shrinkage are shown in figure 6-42.

CONTROLLING CONTRACTION IN SHEET METAL a.b. These stresses in weldments have two major effects: they produce distortion. If contraction is restrained. the parts may be cracked or distorted because of the shrinkage stresses. Thermal expansion is a measure of the linear increase in unit length based on the change in temperature of the material. Parts not heated or not heated as much tend to restrain that portion of the same piece of metal that is heated to a higher temperature.
. This non-uniform heating always occurs in welding. c. This is based on the coefficient of thermal expansion. The coefficient of expansion for the various metals. e. d. Aluminum has one of the highest coefficient of expansion ratios. 6-26. There is a direct relationship between the amount of temperature change and change in dimension. A metal expands or contracts by the same amount when heated or cooled the same temperature if it is not restrained. buckling or warping may occur. Some of the methods used for controlling contraction are described below. Residual stresses that occur when metal is subjected to non-uniform temperature change are called thermal stresses. The welding procedure should be devised so that contraction stresses will be held to a minimum order to keep the desired shape and strength of the welded part. the metals that are heated and cooled are not unrestrained since they are a part of a larger piece of metal which is not heated to the same temperature. When welding. and changes in dimension almost twice as much as steel for the same temperature change. and may cause premature failure in weldments. The restraint caused by the part being non-uniformly heated is the principal cause for the thermal distortion and warpages that occur in welding. If the expansion of the part being welded is restrained.

b. figure 6-43.2 mm) thick is approximately as follows: Metal Steel Brass and Bronze Aluminum In. The spacing of the wedge depends on the type of metal and its thickness. per ft 1/4 to 3/8 3/16 1/4
. In welding long seams. may be used. the contraction of the metal deposited at the joint will cause the edges being welded to draw together and possibly overlap.
c. Spacing for metals more than 1/8 in. (3. The backstep method as shown in view A. which then becomes insignificant to the total pattern of the entire weldment. With the backstep method. This action should be offset by wedging the edges apart as shown in view B. each small weld increment has its own shrinkage pattern. The wedge should be moved forward as the weld progresses. figure 6-43.

thereby decreasing the stresses due to expansion and contraction. (0. Sheet metal under 1/16 in. A weld can be produced in this manner without the addition of filler metal. and tacking at intervals along the seam before welding. Jigs and fixtures may be used to hold members in place for welding.
. These quench plates absorb the heat of welding.Copper Lead
3/16 5/16
d. e. These are usually heavy sections in the vicinity of the seam (fig.
f. The quench plates are heavy pieces of metal clamped parallel to the seam being welded with sufficient space between to permit the welding operation. The heavy sections cool the plate beyond the area of the weld. 6-45).16 cm) thick may be welded by flanging the edges as shown in figure 6-20. Buckling and warping can be prevented by the use of quench plates as shown in figure 6-44.

(0. WELDING DISTORTION AND WARPAGE
. or welding torch. The pipes should be separated by a gap of 1/8 to 1/4 in. kerosene. d. For larger castings. 6-27. Prior to welding gray iron castings.27 to 2. CONTROLLING CONTRACTION AND EXPANSION IN CASTINGS a. spacing as illustrated in figure 6-43. 6-28. (1. small castings can be preheated by means of a torch to a very dull red heat. depending on the size of the pipe being welded. Before welding.g. After welding. e. a reheating and controlled slow cooling or annealing will relieve internal stresses and assure a proper gray iron structure.64 cm). Proper alignment of pipe can be best obtained by tack welding to hold the pieces in place. If the applied heat causes the crack to run. visible in a darkened room. Before welding a crack that extends from the edge of a casting. Such local preheating can be done with a gasoline.54 cm) beyond the visible the crack. The above procedures apply to gray iron castings. 6-46). it is advisable to drill a small hole 1/2 to 1 in. except that less preheat is required for bronze welded castings. it will only extend drill hole. as well as bronze welded castings. If a crack does not extend to the end of a casting. temporary charcoal-fired furnaces built of fire brick and covered with fire resistant material are often used. b. it is advisable to drill a small hole 1/2 to 1 in. (1.32 to 0. expansion and contraction are provided for by preheating. Only local preheating of parts adjacent to the weld is usually necessary (fig.54 cm) beyond each end of the visible crack. In pipe welding. is not practical.
c.27 to 2.

as shown in figure 6-48.
. the metals that are heated and cooled are not unrestrained. as shown in figure 6-49. When heated. it contracts in all directions.a. little motion of the weld is permitted in the direction across the material face (transverse direction) because of the weld joint preparation or stiffening effect of underlying passes. This non-uniform heating and partial restraint is the main cause of thermal distortion and warpage that occur in welding. When it cools. y. if it is not restrained. In the case of a butt weld. the shrinkage stresses are rigid down the length of the weld and across its face. General. In these welds. A weld is usually made progressively. if unrestricted. because they are a part of a larger piece of metal which is not heated to the same temperature. which causes the solidified portions of the weld to resist the shrinkage of later portions of the weld bead. it will contract by the same amount as it expanded. it will expand in the x. Figure 6-47 shows the effects of expansion on a cube of metal. warpage. there will also be transverse residual stresses. metal expands in all directions and when it cools. The portions welded first are forced in tension down the length of the weld bead (longitudinal to the weld) as shown in figure 6-48. For fillet welds. and z directions. there is a direct relationship between the amount of temperature change and the change in dimension of the metal.
b. in welding. As described in paragraph 6-25. The high temperature heat involved in most welding processes is largely responsible for the distortion. When the cube of metal is exposed to a temperature increase. and stresses that occur. A metal expands or contracts by the same amount when heated or cooled the same temperature. However.

As it cools. it acquires higher strength and is now contracting in three directions. For example. If the travel speed is relatively fast. causing shrinkage in one part of the weld to exert eccentric forces on the weld cross section. It is also in its expanded form because of its high temperature. along with the fact that arc temperatures are very similar but the metal melting points are somewhat different. By adjusting the current and travel speed. the less effect differential heating will have. the thermal conductivity of copper is the highest. In either case. Heat would move more quickly through a copper bar than through a steel bar. and this non-uniform strain is seen in macroscopic distortion. Temperature differential has an effect on this. e. The unheated metal tends to resist the cooling dimension changes of the previously molten metal. the exact speed can be determined for a specific joint design so that the root will neither open up nor close together. The weldment strains elastically in response to these stresses. As the metal continues to cool. and there will be movement in the metal adjacent to the weld. and steel about one-fifth that of copper. The arc depositing molten metal is a moving source of heat and the cooling differential is also a moving factor. and they will bow outward and open up the joint. d. Distortion is caused when the heated weld region contracts non-uniformly. f. aluminum is half that amount. With the temperature still declining and each small increment of heated metal tending to contract.c. and the temperature differential would not be so great. Another factor is the travel speed of the heat source or arc. The weld metal is now fused to the base metal. and they work together. it is a momentary situation which continues to change as the weld progresses. the molten metal has little or no strength. The higher the thermal conductivity of the metal. it acquires strength. the effect of the heat of the arc will cause expansion of the edges of the plates. Residual stresses in weldments produce distortion and may be the cause of premature failure in weldments. This is the same as running a bead on the edge of the plate. At the point of solidification. contracting stresses will occur. This physical property must be considered when welding. The distortion may appear in butt joints as both longitudinal and transverse shrinkage or shrinks more plates along contraction and as angular change (rotation)
. but tends to follow the travel of the arc. The temperate differential is determined by thermal conductivity.

These methods include prepositioning the workplaces before welding so that weld distortion leaves them in the desired final geometry. either before or during welding.
g. These effects are shown in figure 6-50. Designing the joint so that weld deposits are balanced on each side of the center
. Since fillet welds are often used in combination with other welds in a weldment. In tension. The angular change produces transverse bending in the the weld length. Control of distortion can be achieved by several methods. Distortion in fillet welds is similar to that in butt welds.when the face of the weld than the root. curling. Transverse and longitudinal shrinkage as well as angular distortion result from the unbalanced nature of the stresses in these welds (fig. or restraining the workplaces so they cannot move and distort during welding. the distortion may be complex. Residual stresses may also contribute to fatigue or corrosion failures. 6-51). When residual stresses and their accompanying distortion are present.
h. Commonly used methods include those which control the geometry of the weld joint. i. buckling may occur at liner compressive loads than would be predicted otherwise. residual stresses may lead to high local stresses in weld regions of low toughness and may result in running brittle cracks which can spread to low overall stress areas. and fracturing at low applied stress levels. Residual stresses and distortion affect materials by contributing to buckling.

but will not change the microstructure or hardness of the weld or heat-affected zone. but also because hard weld heat-affected zones are tempered and made tougher by this procedure. and fabrication cost. but also the reduction of cracks. and other techniques are applied to weldments to accomplish these ends. The welder must consider not only reducing the effects of residual stresses and distortion. and thermal or flame straightening can also be applied. (2) Developing better means for stress relieving and removing distortion. Peening. j. Residual stresses may be eliminated by both thermal and mechanical means. A process or procedure which produces less distortion may also produce more porosity and cracking in the weld zone. the extent of nondestructive testing. the brittle fracture resistance of many steel weldments is improved by thermal stress relief not only because the residual stresses in the weld are reduced. (5) Repetitive identical structure and varying the welding techniques based on measurable warpage. Welding process selection and weld sequence also influence distortion and residual stress. During thermal stress relief. k. (4) The opportunity for balancing welding around the neutral axis. General methods include: (1) Reducing residual stresses and distortion prior to welding by selecting proper processes and procedures. Mechanical stress relief treatments will also reduce residual stresses.
. (3) The time factor for welding and cooling rates when making the various welds. (6) The use or procedures and sequences to minimize weldment distortion. the weldment is heated to a temperature at which the yield point of the metal is low enough for plastic flow to occur and allow relaxation of stress. and distance from the neutral axis in both directions. The following factors should be taken into consideration when welding in order to reduce welding warpage: (1) The location of the neutral axis and its relationship in both directions. Warping and distortion can be minimized by several methods. For example. but not always toward a more uniform distribution across the joint. The mechanical properties of the weldment may also change. porosity. (3) Changing the structural design and the material so that the effects of residual stresses and distortion can be minimized. material degradation due to thermal effects during welding. proofstressing. (2) The location of welds.line is another useful technique. and other discontinuities. Some distorted weldments can be straightened mechanically after welding. size of welds.

which include the following: (1) The use of restraining fixtures. it is important to establish a procedure to minimize warpage. (5) The use of intermittent welding to reduce the volume of weld metal. or many tack welds.
. (4) Balancing welds about the weldment neutral axis or using wandering sequences or backstep welding. (6) The use of proper joint design selection and minimum size. (3) The predistortion or prebending of parts prior to welding. As a general rule. Figure 6-52 shows the order in which the joints should be welded. use preheat or peening. strong backs.
Warpage can be minimized in smaller structures by different techniques. transverse welds should be made before longitudinal welds. The order of joining plates in a deck or on a tank will affect stresses and distortion. (7) As a last resort. (2) The use of heat sinks or the fast cooling of welds.When welding large structures and weldments.

The outer portion of the part cools first. STRESSES AND CRACKING a. When two or more stresses occur in a ductile material. In complicated parts. buckling. it is essentially cast metal. In such cases. brittle fracture. and other brittle metals. In this section. and mild steel yield or stretch while in the plastic or soft conditions. Stress must be relieved after the weld is completed. or metals with low strength at temperatures immediately below the melting point. Parts that cannot move to allow expansion and contraction must be heated uniformly during the welding operation. residual stresses. the stresses occur in three directions. residual stresses occur as a result of the differential cooling that occurs. or are not heated uniformly during the welding operation. The failures that occur without plastic deformation are known as brittle failures. and hot rolled shapes. As the plate becomes thicker. This drawing action produces stresses in and about the weld which may cause warping. weld distortion. since the yield strength and the ultimate strength are nearly the same. WELDING PROBLEMS AND SOLUTIONS
6-29. Upon cooling.Section VI. welding stresses and their effect on weld cracking is explained. they may have undesirable stresses which tend to weaken the finished weld. These precautions are important in welding aluminum. As the parts cool. the material will fail in tension in a brittle manner and the fracture will exhibit little or no pliability. and weld defects. Factors related to weldment failure include weld stresses. d. c. lamellar tearing. This is normal in simple structures with stresses occurring in one direction on parts made of ductile materials. Ductile materials such as bronze. Stress relieving is a process for lowering residual stresses or decreasing their intensity. the weld metal shrinks to a greater extent than the base metal in contact with the weld. exerts a drawing action. weld design. In a thin. the joint will yield in a plastic fashion so that stresses will be reduced to the yield point. Shrinkage stresses due to normal heating and cooling do occur in all three dimensions. there is no yield point for the material. brittle fracture may occur. the stresses may cause warpage. flat plate. cast iron. When simple stresses are imposed on thin. When stresses applied to a joint exceed the yield strength. and the thicker and inner portion cools considerably faster. Where parts being welded are fixed too firmly to permit movement. and the portions that cool later go into a tensile stress mode. In forgings and castings. brittle materials. they contract and pick up strength so that the portions that cool earlier go into a compressive load. forgings. However. or in extremely thick materials. When weld metal is added to the metal being welded. Residual stresses also occur in castings. and are less liable to crack.
. brass. b. high carbon steel. there will be tension stresses at right angles. copper. or other defects. fatigue cracking. e. cracking. and particularly when stresses occur in three directions in a thick material. stresses develop by the shrinking of the weld metal at the joint. and because it is firmly fused. f.

The most common method of measuring stress is to produce weld specimens and then machine away specific amounts of metal. to produce a tight assembly. keeping them within the hole. another tensile stress area. This is because the stresses occur in the longitudinal direction of the weld and perpendicular to the axis of the weld. Cuts are made to reduce or release residual stresses from certain parts of the weld joint. A typical example is the cooling of sleeve bearings to insert them into machined holes. Therefore. and the measurements are taken again. Sleeve bearings are used for heavy. the outer fibers of a part are subject to tensile loading and thus. Normally. With these methods. The residual stresses in a butt weld joint made of relatively thin plate are more difficult to analyze. or its thickness slightly increased. the upset area attempts to contract. Residual stresses occur in all arc welds. and beyond this. Residual stresses are not always detrimental. Large roller bearings are usually assembled to shafts by heating to expand them slightly so they will fit on the shaft. then allowing them to cool. This results in the heated zone becoming stressed in tension. They may have no effect or may have a beneficial effect on the service life of parts. it is possible to establish patterns and actually determine amounts of stress within parts that were caused by the thermal effects of welds. Another method is the use of grid marks or data points on the surface of weldments that can be measured in multiple directions. The
. which are resisting the tensile stress in and adjacent to the weld. This metal is restrained by adjacent cold metal and is slightly upset. The amount of the movement relates to the magnitude of the stresses. The metal close to the weld tends to expand in all directions when heated by the welding arc. there is a tendency to neutralize stress in the outer fibers of the part. h.g. An example of the use of residual stress is in the shrink fit of parts. as illustrated. there is a portion that is compressive. The weldment is gradually and mechanically cut from adjoining portions to determine the change in internal stresses. The two edges are in tensile residual stress with the center in compressive residual stress. during this heating period. with residual compression loading.
j. but is again restrained by cooler metal. When the weld metal starts to cool. When the weld has cooled to room temperature. Slow machinery. A third method utilizes extremely small strain gauges. The movement that occurs is then measured. and allow them to expand to their normal dimension to retain then in the proper location. i. and are subject to compressive residual loading. the weld metal and the adjacent base metal are under tensile stresses close to the yield strength. The residual stresses within the weld are tensile in the longitudinal direction of the weld and the magnitude is at the yield strength of the metal. Figure 6-53 shows residual stresses in an edge weld.

at which the yield strength of the metal is greatly reduced. the first weld or root pass originally creates a tensile stress. This method also makes the stress pattern at the weld area more uniform.base metal adjacent to the weld is also at yield stress. it will contract as it solidifies and gain strength as the metal cools. The weldment is then allowed to cool slowly and uniformly so that the temperature differential between parts is minor. the weldment is uniformly heated to an elevated temperature. the residual stresses quickly fall to zero. This will not eliminate residual stresses. and this creates tensile stresses at and adjacent to the weld. as described below: (1) If the weld is stressed by a load beyond its yield. l. it tends to pull. In heavier weldments when restraint is involved. Further from the weld or bead. (2) High residual stresses can be reduced by stress relief heat treatment. the metal must remain in equilibrium. causing them to expand. and the root pass will have tensile residual stress. As each weld is made. With heat treatment. but are still located at the yield point of the metal. As passes are made until the weld is finished. change to compression. The
. movement is not possible. In a multipass single-groove weld. but will create a more uniform stress pattern. and fourth passes contract and cause a compressive load in the root pass. Another way to reduce high or peak residual stresses is by means of loading or stretching the weld by heating adjacent areas. strength plastic deformation will occur and the stresses will be more uniform. the relationship is different because of the many passes of the heat source. the center of the plate in compression. and residual stresses are of a higher magnitude. third. The heat reduces the yield strength of the weld metal and the expansion will tend to reduce peak residual stresses within the weld. The second. and in order to maintain balance. Except for single-pass.
k. Residual stresses can be decreased in several ways. When moving away from the weld into the base metal. and therefore compressive stresses occur. parallel to the weld and along most of the length of the weld. As it contracts. the compressive and tensile residual stresses can only be estimated. The residual stresses in the weld at right angles to the axis of the weld are tensile at the center of the plate and compressive at the ends. simple joint designs. This is shown in figure 6-54. the top passes will be in tensile load. For thicker materials when the welds are made with multipasses.

q. it will have enough strength to withstand cracking tendencies. o. Residual stresses also contribute to weld cracking. When a weld is made with higher-carbon or higher-alloy base material. including the stiffness or rigidity of the weldment itself. Shrinkage will also occur quickly. it will cool quickly. and if the parts being welded cannot move with respect to one another and the weld metal has insufficient ductility. and cracking can occur. If the base metal being joined is cold and the weld is small. including the following: (1) Insufficient weld metal cross section to sustain the loads involved. it may not have enough ductility to cause plastic deformation. Restraint and residual stresses are the main causes of weld cracking during the fabrication of a weldment. (2) Insufficient ductility of weld metal to yield under stresses involved. n. The resulting weld metal has higher carbon and alloy content. In addition. Weld cracking sometimes occurs during the manufacture of the weldment or shortly after the weldment is completed. weld may crack in the weld metal or in the base metal adjacent to welds metal.
. Alloy or carbon content of base material can also affect cracking. or the weld should be made with sufficient cross-sectional area so that as it cools. Movement of welds may impose high loads on other welds and cause them to crack during fabrication. It may have higher strength.cooling will be uniform and a uniform low stress pattern will develop within the weldment. but it has less ductility. and will cool more or less uniformly from that temperature and so reduce peak residual stresses. since the entire weldment is at a relatively high temperature. p. As it shrinks. Typical weld cracks occur in the root pass when the parts are unable to move. the cooling rate will be lower and cracking can be eliminated. Cracking occurs due to many reasons and may occur years after the weldment is completed. a crack will result. m. If the parts being joined are preheated even slightly. Weld metal shrinks as it cools. and cracking may occur. particularly those subject to low-temperature when the failure of the weldment will endanger life. usually in the heat-affected zone. A more ductile filler material should be used. Weld cracking that occurs during or shortly after the fabrication of the weldment can be classified as hot cracking or cold cracking. (3) Under-bead cracking due to hydrogen pickup in a hardenable type of base material. Weld restraint can come from several factors. (3) High-temperature preheating can also reduce residual stress. a certain amount of the base material is melted and mixed with the electrode to produce the weld metal. Rapid cooling of the weld deposit is also responsible for weld cracking. Welds crack for many reasons. Cracks are not permitted in most weldments. Cracks are the most serious defects that occur in welds or weld joints in weldments.

This type of cracking can be reduced by increasing preheat. The presence of higher-carbon materials or high alloy in the base metal can also be a cause. it will reject the hydrogen. Table 6-1 lists preheating temperatures of specific metals. This involves surf acing the weld face of the joint with a weld metal that is much lower in carbon or alloy content than the base metal.
. Total joint strength must still be great enough to meet design requirements. so a more ductile weld deposit is made.64 cm) thick should be preheated for 15 minutes at the stress relieving temperature. (3) Preheating facilitates welding in many cases. usually with compressed air and a roughing or peening tool. When using cellulose-covered electrodes or when hydrogen is present because of damp gas.r. heating the completed weld for 1 hour per 1. In stress relieving mild steel. steel 1/4 in. Hydrogen pickup in the weld metal and in the heat-affected zone can also cause cracking. (0. (1) Stress relieving in steel welds may be accomplished by preheating between 800 and 1450°F (427 and 788°C). Small pieces. On this basis.00 in. The use of preheat reduces the rate of cooling. which causes cracking. When welding highalloy or high-carbon steels. s. and then slowly cooling. damp flux. (2) Peening is another method of relieving stress on a finished weld. or hydrocarbon surface materials. such as butt welded high speed tool tips. may be annealed by putting them in a box of fire resistant material and cooling for 24 hours. reducing restraint. However. As the metal cools. (2. which tends to decrease the possibility of cracking. cracking can occur. Stress Relieving Methods. Cooling under some conditions may take 10 to 12 hours. It prevents cracking in the heat affected zone. and eliminating hydrogen from the arc atmosphere. and if there is enough restraint. If proper preheating times and temperatures are used. excessive peening may cause brittleness or hardening of the finished weld and may actually cause cracking. the cause is usually hydrogen pickup in the weld metal and the heat-affected zone of the base metal. the hydrogen in the arc atmosphere will be absorbed in the molten weld metal and in adjoining high-temperature base metal. When cracking is in the heat-affected zone or if cracking is delayed. the buttering technique can be used to prevent cracking. particularly on the first passes of the weld metal. Underbead cracking can be reduced by the use of low-hydrogen processes and filler metals. depending on the material. the cooling rate is slowed sufficiently to prevent the formation of hard martensite. t.54 cm) of thickness is common practice. The weld is then made between the deposited surfacing material and avoids the carbon and alloy pickup in the weld metal.

u.
. (f) When welding steels with a high carbon. (g) When steel being welded tends to harden when cooled in air from the welding temperature. The following general procedures can be used to relieve stress and to reduce cracking: (1) Use ductile weld metal. (b) When the diameter of the welding rod is small in comparison to thickness of the metal being joined. low manganese. (e) When there is a great difference in mass of the parts being welded.(4) The need for preheating steels and other metals is increased under the following conditions: (a) When the temperature of the part or surrounding atmosphere is at or below freezing. or other alloy content. (c) When welding speed is high (d) When the shape and design of the parts being welded are complicated.

storage tanks. a. However. Failures of these types of structures occurred before welding was widely used and still occur in unwelded structures today.(2) Avoid extremely high restraint or residual stresses. 6-30. including brittle fracture. IN-SERVICE CRACKING Weldments must be designed and built to perform adequately in service. pressure vessels. There is no reduction of area at the fracture (fig.
(2) Brittle fracture occurs by cleavage across individual crystals. The fracture exposes the granular structure. forgings. ships. There are four specific types of failures. Welding has sometimes been blamed for the failure of large engineering structures. (4) Utilize low-alloy and low-carbon materials.
. they will probably crack. (7) When welds are too small for the service intended. lamellar tearing. and there is little or no stretching or yielding. There is a definite stretching or yielding and a reduction of cross-sectional area at the fracture (fig. it is still important to make weldments and welded structures as safe against premature failure of any type as possible. but it should be noted that failures have occurred in riveted and bolted structures and in castings. fatigue fracture. and penstocks. The risk of failure of a weldment is relatively small. 6-55). (3) Revise welding procedures to reduce restraint. as well as other types of construction. (5) Reduce the cooling rate by use of preheat. Brittle Fracture. 6-56). ductile and brittle. The welder should ensure that the size of the welds are not smaller than the minimum weld size designated for different thicknesses of steel sections. (6) Utilize low-hydrogen welding processes and filler metals. hot rolled plate and shapes. but failure can occur in structures such as bridges. and stress corrosion cracking. Fracture can be classified into two general categories. (1) Ductile fracture occurs by deformation of the crystals and slip relative to each other.

Ductile fractures have a shear mode of crystalline failure. a notch or defect. Some of these factors can be eliminated and thus reduce the possibility of brittle fracture. Brittle fracture is therefore more similar to the fracture of glass than fracture of normal ductile materials. They are growth marking. In fact. The following conditions must be present for brittle fracture to occur: low temperature. Brittle or cleavage fractures have either a granular or a crystalline appearance. A combination of conditions must be present at the same time for brittle fracture to occur. a relatively high rate of loading. fracture surface texture and appearance. (7) The third factor is fracture surface and texture. (4) There are four factors that should be reviewed when analyzing a fractured surface.
. This means that the fracture which propagated across the section changed its mode of fracture. Brittle fractures usually have a point of origin. and usually a considerable necked down area in the case of a ductile fracture. Ductile fractures often appear to have failed in shear as evidenced by all parts of the fracture surface assuming an angle of approximately 45 degrees with respect to the axis of the load stress.(3) It is possible that a broken surface will display both ductile and brittle fracture over different areas of the surface. mild steel may exhibit good toughness characteristics at roan temperature. The apex of the chevron appearing on the fractured surface always points toward the origin of the fracture and is an indicator of the direction of crack propagation. The chevron pattern will help locate this point. and the steels fracture at stresses below the normal yield strength for steel. Mild steels. (5) Growth markings are one way to identify the type of failure. The microstructure of the metal also has an effect. (9) One characteristic of brittle fracture is that the steel breaks quickly and without warning. The fractures increase at very high speeds. and amount of yielding or plastic deformation at the fracture surface. fracture mode. may fail in a brittle manner. and triaxial stresses normally due to thickness of residual stresses. which show a normal degree of ductility when tested in tension as a normal test bar. There is little or no deformation for a brittle fracture. (6) Fracture mode is the second factor. Fatigue failures are characterized by a fine texture surface with distinct markings produced by erratic growth of the crack as it progresses. The surface texture is silky or fibrous in appearance. The chevron or herringbone pattern occurs with brittle or impact failures. (8) An indication of the amount of plastic deformation is the necking down of the surface.

This raises the transition temperature of the steel. The z direction acts as a restraint at the base of the notch. the degree of restraint in the through direction is higher. or heating to the proper temperature and cooling slowly. (13) Triaxial stresses are more likely to occur in thicker material than in thin material.(10) Temperature is an important factor which must be considered in conjunction with microstructure of the material and the presence of a notch. fabrication operations on steel. which is known as the transition temperature. A steel in the as-rolled condition will have a higher transition temperature or liner toughness than the same steel in a normalized condition. (15) Welding tends to accentuate Some of the undesirable characteristics that contribute to brittle fracture. The material under load behaves elastically. This is why brittle fracture is more likely to occur in thick plates or complex sections than in thinner materials. Metal adjacent to the end of the crack which does not carry load will not undergo a reduction of area since it is not stressed. The thermal treatment resulting from welding tends to reduce the toughness of the steel or to raise its transition temperature in the heat– affected zone. Thicker plates also usually have less mechanical working in their manufacture than thinner plates and are more susceptible to lower ductility in the z axis. The microstructure and chemistry of the material in the center of thicker plates have poorer properties than the thinner material. which receives more mechanical working. Microstructure of a steel depends on the chemical composition and production processes used in manufacturing it. does not allow sufficient time for the normal slip process to occur. produces a grain refinement which provides for higher toughness. The monolithic structure of a weldment means that more energy is locked up and there is the
. It is. occurs near a notch in heavy thick material. Unfortunately. When the rate of loading. and flame cutting. the material at the base of the notch is subjected very suddenly to very high stresses. and for thicker material. Impact testing of steels using a standard notched bar specimen at different temperatures shows a transition from a ductile type failure to a brittle type failure based on a lowered temperature. a restraint which helps set up triaxial stresses at the base of the notch or the end of the crack. in effect. It is concentrated at this point and little or no yielding will occur. (14) The microstructure of the material is of major importance to the fracture behavior and transition temperature range. A crack will not carry stress across it. Stress levels much higher than normal occur at this point and contribute to starting the fracture. (11) The notch that can result from faulty workmanship or from improper design produces an extremely high stress concentration which prohibits yielding. allowing a stress level beyond the normal yield point. such as hot and cold forming. punching. from impact or shock stresses. Normalizing. The effect of this is often complete and rapid failure of a structure and is what makes brittle fracture so dangerous. affect the original microstructure. The high rate of strain. (12) The rate of loading is the time versus strain rate. which is a result of impact or shock loading. and the load is transmitted to the end of the crack.

This type of failure is called a fatigue failure. The fracture surface also tends to become rougher as the rate of propagation of the crack increases. (1) Fatigue failure is the formation and development of a crack by repeated or fluctuating loading. and defects in weld joints can be the nucleus for the notch or crack that will initiate fracture. Structures sometimes fail at nominal stresses considerably below the tensile strength of the materials involved. When sudden failure occurs. (16) Brittle fractures can be reduced in weldments by selecting steels that have sufficient toughness at the service temperatures. and type of material. The materials involved were ductile in the normal tensile tests. the rate of loading. Most of these failures development after the structure had been subjected to a large number of cycles of loading. Figure 6-57 shows the characteristic fatigue failure surface. Fatigue Failure. it is because the crack has increased enough to reduce the load-carrying capacity of the part. normalizing. These rings show the propagation of the crack. Design notches must be eliminated and notches resulting from poor workmanship must not occur.possibility of residual stresses which may be at yield point levels. Repeated loading causes progressive enlargement of the fatigue cracks through the material. Internal cracks within the welds and unfused root areas must be eliminated. which might be related to periods of high stress followed by periods of inactivity. The rate at which the fatigue crack increases depends upon the type and intensity of stress as well as other factors involving the design. The monolithic structure also causes stresses and strains to be transmitted throughout the entire weldment. or any method of reducing locked-up stresses will reduce the triaxial yield strength stresses within the weldment. but the failures generally exhibited little or no ductility. The transition temperature should be below the service temperature to which the weldment will be subjected. b. (2) The fracture surface of a fatigue failure is generally smooth and frequently shins concentric rings or areas spreading from the point where the crack initiated.
. but they will not fail until the load-carrying area is sufficiently reduced. Fatigue cracks may exist in some weldments. Heat treatment.

It is therefore important to determine those factors which adversely affect the fatigue life of a weldment. including excessive reinforcement. These can be alternating cycles from tension to compression. Fatigue is a cumulative process and its effect is in no way healed during periods of inactivity. Many structures. For practical purposes. These changes may range from simple cyclic fluctuations to completely random variations. it is important to consider the number of times the weldment is subjected to the cyclic loading. and total design and design details. Fatigue test specimens are machined and polished. cycle curves. slag inclusions. joints may not have full penetration because of an unfused root. Anything that can be done to smooth out the stress flow in the weldment will reduce stress concentrations and make the weldment less subject to fatigue failure. Welds designed for full penetration might not have complete penetration because of workmanship factors such as cracks. and therefore contain a stress concentration. Testing machines are available for loading metal specimens to millions of cycles. undercut. The last factor is controllable in the design and manufacture of the weldment. or pulsating loads with pulses from zero load to a maximum tensile load. The weld defects mentioned previously. loading is considers in millions of cycles. This prohibits uniform stress distribution. the stress of which remains relatively constant. This is based on statically loaded structures. either tensile or compressive. Lamellar Tearing. and is found in rolled steel plate weldments. Total design with this in mind and careful workmanship will help to eliminate this type of problem. the structure must be designed for dynamic loading and considered with respect to fatigue stresses. In this type of loading. usually outside the heat-affected zone and generally parallel to the weld fusion boundary. In addition to the loadings. the stress level and nature of stress variations. and the results obtained on such a specimen may not correlate with actual service life of a weldment. if the reinforcement is excessive. and when parts are attached by welding. a portion of the stress will flow through the reinforced area and will not be uniformly distributed. c. however. will contribute to the stress concentration factor. or from a zero load to a compressive load. are subject to other than static loads in service. Weld joints can be designed for uniform stress distribution utilizing a fullpenetration weld. or negative reinforcement. The results are plotted on stress vs. The tearing always lies within the base metal. Even with a full-penetration weld. the number of loading cycles. Lamellar tearing is a cracking which occurs beneath welds. they may produce sudden changes of section which contribute to stress concentrations under normal types of loading. (4) The varying loads involved with fatigue stresses can be categorized in different manners. or loads can be high and rise higher. One reason fatigue failures in welded structures occur is because the welded design can introduce more severe stress concentrations than other types of design. This type of cracking has
. which show the relationship between the stress range and the number of cycles for the particular stress used. (5) The possibility of a fatigue failure depends on four factors: the material used.(3) Many structures are designed to a permissible static stress based on the yield point of the material in use and the safety factor that has been selected. but in other cases. A weld also forms an integral part of the structure. and incomplete penetration.

shining a tee joint. the lamination type crack is removed and replaced with weld metal. this type of failure was probably occurring and was not found. It is only when welds subjected the base metal to tensile loads in the z. the section can actually come out and separate from the main piece of metal. This type of crack can only be found with ultrasonic testing or if failure occurs. Figure 6-58 shows how lamellar tearing will come to the surface of the metal. Before the advent of ultrasonic testing. the lower strength of rolled steel in the through direction was recognized and the structural code prohibited z-directional tensile loads on steel spacer plates. is a more common type of lamellar tearing. which is much more difficult to find. or through. the crack does not cane to the surface and is under the weld.been found in corner joints where the shrinkage across the weld tended to open up in a manner similar to lamination of plate steel. Figure 6-59. In this case. For many years.
. direction of the rolled steel that the problem is encountered. In these cases.

(5) Arc welding processes having higher heat input are less likely to create lamellar tearing. Lamellar tearing can be overcome in corner joints by placing the bevel for the joint on the edge of the plate that would exhibit the tearing rather than on the other plate. A stress placed in the z direction triggers the tearing. It is primarily the low strength of the material in the z. The thermal heating and stresses resulting from weld shrinkage create the fracture. stress through the joint across the plate thickness or in the z direction due to weld orientation in which the fusion line beneath the weld is roughly parallel to the lamellar separation. In tee joints. Balanced welds on both sides of the joint present less risk of lamellar tearing than large single-sided welds. Preheat
. Lamellar tearing is not associated with the under-bead hydrogen cracking problem. Butt joints rarely are a problem with respect to lamellar tearing since the shrinkage of the weld does not set up a tensile stress in the thickness direction of the plates. (4) Joint details can be changed to avoid the possibility of lamellar tearing. There are only certain plates where the concentration of inclusions are coupled with the unfavorable shape and type that present the risk of tearing. and the condition of the steel. (2) Lamellar tearing can occur during flame-cutting operations and also in cold-shearing operations. and poor ductility of the material in the z. These are strains in the through direction of the plate caused by weld metal shrinkage in the joint and increased by residual stresses and by loading. In general. Also. Deposited filler metal with lower yield strength and high ductility also reduces the possibility of lamellar tearing. direction. or through. or through. and are more apt to occur in thicker materials and in higher-strength materials. but on occasion will occur at a period months later. Lamellar tearing at the corner joints is readily detected on the exposed edge of the plate. joint design. (3) Only a very small percentage of steel plates are susceptible to lamellar tearing. corner joints are common in box columns. This may be because of the fewer number of applications of heat and the lesser number of shrinkage cycles involved in making a weld.(1) Three conditions must occur to cause lamellar tearing. These conditions rarely occur with the other two factors mentioned previously. three situations must occur in combination: structural restraint. It can occur soon after the weld has been made. double-fillet weld joints are less susceptible than fullpenetration welds. direction that contributes to the problem. This is shown by figure 6-60. the tears are under the heat-affected zone.

and for this reason. General. (3) Graphitization is another type of cracking. (2) Stress corrosion cracking in steels is sometimes called caustic embrittlement. This is an extreme solution and should only be used as a last resort. Close inspection must be maintained on highly stressed areas. and nickel. These steels must be welded with filler metals of the same composition. cause excessive spatter. it cannot retain all of the hydrogen and is forced out of solution. Stress corrosion cracking and delayed cracking due to hydrogen embrittlement can both occur when the weldment is subjected to the type of environment that accentuates this problem. carbon molybdenum steels are normally used in high-temperature power plant service. and if enough hydrogen is present. and can also impair the quality
. d. The concentration of hydrogen and the stresses resulting from it when coupled with residual stresses promote cracking. caused by long service life exposed to thermal cycling or repeated heating and cooling. As the metal solidifies. Stress corrosion cracking will occur if the concentration of the caustic solution in contact with the steel is sufficiently high and if the stress level in the weldment is sufficiently high. Cracking will be accelerated if the weldment is subjected to thermal stresses due to repeated heating and cooling. The high level of tension stresses can be created by loading or by high residual stresses. it will cause cracking in the weld or the heat-affected zone. Liquid or molten steel will absorb large quantities of hydrogen.and stress relief heat treatment are not specifically advantageous with respect to lamellar tearing. It will often occur in carbon steels deoxidized with aluminum. 6-31. Arc blow is the deflection of an electric arc from its normal path due to magnetic forces. This may cause a breakdown of carbides in the steel into small areas of graphite and iron. It will usually adversely affect appearance of the weld. By observing the design factors mentioned above. This type of cracking takes place when hot concentrated caustic solutions are in contact with steel that is stressed in tension to a relatively high level. This situation can be reduced by reducing the stress level and the concentration of the caustic solution. This formation of graphite in the edge of the heat-affected area exposed to the thermal cycling causes cracking. ARC BLOW a. The addition of molybdenum to the steel tends to restrict graphitization. The buttering technique of laying one or more layers of low strength. Various inhibitors can be added to the solution to reduce the concentration. such as steel. highductility weld metal deposit on the surface of the plate stressed in the z direction will reduce the possibility of lamellar tearing. Stress Corrosion Cracking. but can also be encountered when welding nonmagnetic materials. It is mainly encountered with dc welding of magnetic materials. (1) Delayed cracking is caused by hydrogen absorbed in the base metal or weld metal at high temperatures. the lamellar tearing problem is reduced. The hydrogen coming out of the solution sets up high stresses. iron. These cracks develop over a period of time after the weld is completed.

which state that like poles repel and opposite poles attract. it produces a magnetic flux in circles around the conductor in planes perpendicular to the conductor and with their centers in the conductor. This magnetic field is the same as that produced by an electromagnet. flowing through the electrode and the base metal. sets up magnetic fields around the electrode. Arc blow can become so severe that it is impossible to make a satisfactory weld. Direct current. As the self-induced field around the arc is attracted and repelled. Moving the flux field surrounding the arc and introducing an external-like polarity field roves the arc magnetically. the fingers point in the direction of the flux. The right-hand rule is used to determine the direction of the magnetic flux. It is often encountered when using the shielded metal arc welding process with covered electrodes. It is also a factor in semiautomatic and fully automatic arc welding processes. the arc is parallel or in line with the centerline of the electrode and takes the shortest path to the base plate. When an electric current passes through an electrical conductor. Likewise. the forces on the arc are no longer equal and the arc is deflected by the strongest force. It can be oscillated by transverse magnetic fields or be made to deflect in the direction of travel. The direction of the magnetic flux produces polarity in the magnetic field. The electrical-magnetic relationship is used in welding applications for magnetically moving. which tries to maintain symmetry within its own selfinduced magnetic field. If the symmetry of this magnetic field is disturbed. it may be deflected from one side to the other. The magnetic field in the vicinity of the welding arc is the field produced by the welding current which passes through it from the electrode and to the base metal or work. the magnetic fields are also much stronger. the same as the north and south poles of a permanent magnet.
b. apply in this situation. As long as the magnetic field is symmetrical. It states that when the thumb of the right hand points in the direction in which the current flows (conventional flow) in the conductor.of the weld. Welding current is much higher than the electrical current normally encountered. c. there is no unbalanced magnetic force and no arc deflection. The welding arc is an electrical conductor and the magnetic flux is set up surrounding it in accordance with the right-hand rule. which deflect the arc from its intended path. Under these conditions. Figure 6-61 shows the effect of ground location on magnetic arc blow. Arcs can also be made to rotate around the periphery of abutting pipes by means of
. d. Back blow is encountered when welding toward the ground near the end of a joint or into a corner. or oscillating. it tends to move the arc column. however. The welding arc is usually deflected forward or backward of the direction of travel. This is a self-induced circular magnetic field which surrounds the arc and exerts a force on it from all sides according to the electrical-magnetic rule. The rules of magnetism. The gas tungsten arc is deflected by means of magnetic flux. Forward blow is encountered when welding away from the ground at the start of a joint. Magnetic oscillation of the gas tungsten welding arc is used to widen the deposition. the welding arc. Oscillation is obtained by reversing the external transverse field to cause it to attract the field surrounding the arc.

The lines of force are concentrated together on the inside of the angle of the current path through the electrode and the work. e. Welding cur-rent passes through the electrode lead. This is toward the weaker force and is opposite the direction of the current path. The magnetic flux will pass through a magnetic material such as steel much easier than it will pass through air. the magnetic field is also reversed.
. the electrode holder to the welding electrode. Longer arcs are moved more easily than short arcs. away from the path of the current through the work.rotating magnetic fields. and the magnetic flux path will tend to stay within the steel and be more concentrated and stronger than in air. it will tend to move the self-induced field surrounding the arc and thus deflect the arc itself. and the fact that the lines of force are perpendicular to the path of the welding current creates a magnetic unbalance. The amount of magnetic flux to create the movement must be of the same order as the flux field surrounding the arc column. At this point the current changes direction to pass to the work lead connection. If the welding current is reversed. then through the arc into the base metal. which produces a force on the stronger side and deflects the arc to the left. Whenever the symmetry of the field is disturbed by some other magnetic force. Consequently. Except under the most simple conditions. and are spread out on the outside angle of this path. There is always an unbalance of the magnetic field around the arc because the arc is roving and the current flow pattern through the base material is not constant. then through the work lead back to the welding machine. the magnetic field is much stronger on the side of the arc toward the work lead connection than on the other side. the self-induced magnetic field is not symmetrical throughout the entire electric circuit and changes direction at the arc. The direction of this force is the same regardless of the direction of the current. the change of direction is relatively abrupt. but the direction of the magnetic force acting on the arc is always in the same direction. This is shown by figure 662. At the point the arc is in contact with the work.

The alternating magnetic field is a roving
. As the weld approaches the end. and at times may meet at right angles. Reduction of arc blow is reduced because the alternating current sets up other currents that tend to either neutralize the magnetic field or greatly reduce its strength. The polarity or direction of flow of the current does not affect the direction of these forces nor the resultant force. the lines of force must cross the air gap or root opening. Back blow can occur right up to the end of the joint. h. Near the start end of the joint the lines of force are crowded together and will tend to stay within the steel. By analyzing the path of the welding current through the electrode and into the base metal to the work lead. These forces may add or subtract from each other. where the weld has been made the lines of force go through steel. it is possible to determine the resultant forces and predict the resulting arc deflection or arc blow. At this point.
g. Since the work lead is immediately under the arc and moving with the arc. Alternating current varies between maximum value of one polarity and the maximum value of the opposite polarity. In addition. the magnetic path in the work will not be concentric about the point of the arc. Back blow can become extremely severe right at the very end of the joint. The second factor that keeps the magnetic field from being symmetrical is the fact that the arc is moving and depositing weld metal. back blow may be encountered. because the lines of force take the easiest path rather than the shortest path. the flux ahead of the arc becomes more crowded. The magnetic field surrounding the alternating current conductor does the same thing. the total force tending to cause the arc to deflect is a combination of these two forces. This is because the flux soon finds an easy path through the weld metal. The magnetic field is more intense on the short end and the unbalance produces a force which deflects the arc to the right or toward the long end. When welding with direct current. the arc moves from one end of the joint to the other and the magnetic field in the plates will constantly change. Where the weld is not made.f. Forward blow exists for a short time at the start of a weld. the arc is influenced mainly by the flux in front of it as this flux crosses the root opening. however. and analyzing the magnetic field within the base metal. then diminishes. increasing the back blow. the lines of force will be separated since there is more area. Once the magnetic flux behind the arc is concentrated in the plate and the weld. i. ac welding does not completely eliminate arc blow. The use of alternating current for welding greatly reduces the magnitude of deflection or arc blow. Toward the finish end of the joint. This is shown by figure 6-63. As a weld is made joining two plates.

In sane cases. These induced currents are called eddy currents. The location of magnetic material with respect to the arc creates a magnetic force on the arc which acts toward the easiest magnetic path and is independent of electrode polarity. Alternating current cannot be used for all welding applications and for this reason changing from direct current to alternating current may not always be possible to eliminate or reduce arc blow. When alternating current is used for welding. according to the induction principle. They always flow from the opposite direction as shown by figure 6-64. These currents are alternating currents of the same frequency as the arc current and are in the part of the work nearest the arc. eddy currents are induced in the workpiece.
j. (3) Arc blow is not as severe with alternating current because the induction principle creates current flow within the base metal which creates magnetic fields that tend to neutralize the magnetic field affecting the arc. (1) Arc blow is caused by magnetic forces. It is best to have the work lead connection at the starting point of the weld. The resultant magnetic force is opposite in direction to the current from the arc to is independent of welding current polarity. This is particularly true in electroslag welding where the work lead should be connected to the starting sump. therefore. The induced magnetic forces are not symmetrical about the magnetic field surrounding the path of the welding current. the intensity and the direction of the force changes. (2) Welding current will take the easiest path but not always the most direct path through the work to the work lead connection. They produce a magnetic field of their own which tends to neutralize the magnetic field of the arc current.field which induces current in any conductor through which it passes. On occasion. The location of the work connection is of secondary importance. Summary of Factors Causing Arc Blow. (4) The greatest magnetic force on the arc is caused by the difference resistance of the magnetic path in then the base metal around the arc.
. which produce magnetic fields and reduce the intensity of the field acting on the arc. leads can be connected to both ends. Currents are induced in nearby conductors in a direction opposite that of the inducing current. The location of the easiest magnetic path changes constantly as welding progresses. but may have an effect on reducing the total magnetic force on the arc. the work lead can be changed to the opposite end of the joint.

WELD FAILURE ANALYSIS
. (12) Change to ac. This can be accomplished by wrapping several turns of welding lead around the workpiece. This can be accomplished by runoff tabs. particularly when the base metal has been handled by magnet lifting cranes. The hold-down clamps and backing bars must fit closely and tightly to the work. Residual magnetism in heavy thick plates handled by magnets can be of such magnitude that it is almost impossible to make a weld. Magnetic structure of the fixture can affect the magnetic forces controlling the arc. (8) If forward blow causes trouble. and weld toward a heavy tack weld.k. starting plates. The welding fixture can be a source of arc blow. which may require a change in electrode classification (13) Wrap the ground cable around the workpiece in a direction such that the magnetic field it sets up will counteract the magnetic field causing the arc blow. In general. (10) Reduce the welding current. therefore. and backing strips. (14) Another major problem can result from magnetic fields already in the base metal. (7) If to back blow is the problem. (9) Position the electrode so that the arc force counteracts the arc blow. wrap the part with welding leads to help overcome their effect. (1) The magnetic forces acting on the arc can be modified by changing the magnetic path across the joint. copper or nonferrous metals should be used. place the ground connection at the start of welding. (4) Use as short an arc as possible so that there is less of an arc for the magnetic forces to control. In this case. Minimizing Arc Blow. or stress relieve or anneal the parts. (6) Place ground connections as far as possible from the joints to welded. an analysis with respect to fixturing is important. 6-32. (11) Use the backstep sequence of welding. (3) Arc blow is usually more pronounced at the start of the weld seam. as well as the welding sequence. Attempt to demagnetize the parts. (2) An external magnetic field produced by an electromagnet may be effective. a magnetic shunt or runoff tab will reduce the blow. place the ground connection at the end of the joint to be welded. large tack welds. (5).

along with design stress data originally used in designing the product. and service use. Studies should also be made microscopically in those situations in which it would lead to additional information. Photographs should be taken. investigate all factors that could remotely be considered. should also be noted and investigated. and evaluate all this information to find the reason for the failure. preferably in color. but also all negative responses that may be learned about the failure. repairs in and during manufacturing and in service. overloads. Each failed part should be thoroughly investigated to determine what bits of information can be added to the total picture. there are occasional failures of noncritical welds and weldments that should also be investigated. as with a large structure. b. and all other factors. fracture texture appearance. but failures of large engineered structures do occur occasionally. The following four areas of interest should be investigated to determine the cause of weld failure and the interplay of factors involved: (1) Initial observation. General. Investigators should gather all information concerning specifications. Original drawings should be obtained and marked showing failure locations. of all parts. (4) Failure assumptions. structures. component design. (2) Background data. Failures of insignificant parts can also lead to advances in knowledge and should be done objectively. failure surfaces. In the same manner. welding procedures. The investigator should list not only all positive facts and evidence that may have contributed to the failure. final location of component debris. manufacturing. weld schedules. Any other defects in the structure that are apparent. and the actual mode of the failure. Investigators should make tests to verify that the material in the failed parts actually possesses the specified composition. cyclic loading. An objective study must be made of any failure of parts or structures to determine the cause of the failure. including operating temperatures. fabrication methods. maintenance. Efforts should be made to obtain facts pertinent to all possible failure modes. It is sometimes important to know what specific things did
.a. and dimensions. Catastrophic failures of major structures are usually reported whenever they occur. Each failure and subsequent investigation will lead to changes that will assure a more reliable product in the future. the conditions that led up to the failure. drawings. (3) Laboratory studies. An objective study of failure should utilize every bit of information available. Witnesses to the failure should all be interviewed and all information determined from them should be recorded. and abuse. Particular attention should be given to environmental details. mechanical properties. or operating practice. This is done by investigating the service life. even though they might not have contributed to the failure. that will eliminate similar failures in the future. Fracture surfaces can be extremely important. Once the reason is determined it can then be avoided. normal service loads. The detailed study by visual inspection of the actual component that failed should be made at the failure site as quickly as possible. Failure investigation often uncovers facts that lead to changes in design. The results of investigations of these failures are usually reported and these reports often provide information that is helpful in avoiding future similar problems. Only rarely are there failures of welded structures.

(2) Failure due to improper processing or improper workmanship. (2) Failures can be caused by faulty processing or poor workmanship that may be related to the design of the weld joint. lack of fusion.not happen or what evidence did not appear to help determine what happened. d. Failures can be attributed to poor fabrication practice such as the elimination of a root opening. c. The product might be exposed to an environment for which it was not designed. Examination of catastrophic and major failures has led the welding industry to appreciate the following facts: (1) Weldments are monolithic in character. which will contribute to incomplete penetration. or the wrong material may have been specified for producing the part. create stress concentration. Normal wear and abuse to the equipment may have result-ed in reducing sections to the degree that they no longer can support the load. there may be other types of situations such as poor maintenance. (3) Failure due to deterioration during service. e. (3) Failure due to deterioration during service can cause overload. and accidental conditions beyond the user’s control. or cracks. Failure cause can usually be classified in one of the following three classifications: (1) Failure due to faulty design or misapplication of material. poor repair techniques involved with maintenance. or the weld joint design can be proper but the quality of the weld is substandard. (2) Anything welded onto a structure will carry part of the load whether intended or not. (3) Abrupt changes in section. Corrosion due to environmental conditions and accentuated by stress concentrations will contribute to failure. Conclusion. The following is a summary of the above three situations: (1) Failure due to faulty design or misapplication of the material involves failure due to inadequate stress analysis. which may be difficult to determine. The data should be tabulated and the actual failure should be synthesized to include all available evidence. The poor quality weld might include such defects as undercut. In addition. or a mistake in design such as incorrect calculations on the basis of static loading instead of dynamic or fatigue loading. Ductile failure can be caused by a load too great for the section area or the strength of the material. There is also the possibility that the incorrect filler metal was used for welding the part that failed. Under normal
. either because of adding a deckhouse or removing a portion of the deck for a hatch opening. Brittle fracture may occur from stress risers inherent in the design.

These are welding over painted surfaces and painting of welds. and in other flame cutting is done on painted base metal. the dryness of the paint. There are two other welding problems that require some explanation and solutions. b. In sane shipyards a different color paint is used for different classes of steel. If the weld breaks at the interface of the plate with the paint it is obvious that the paint is not compatible with the weld. (1) In the shipbuilding industry and several other industries. (3) Paint compatibility varies according to the composition of the paint. CAUTION Cutting painted surfaces with arc or flame processes should be done with caution. Welding over paint is discouraged. The fillet break test can be used to determine compatibility. failure can result. Anything that contributes to deoxidizing the weld such as aluminum. In every code or specification. (4) The fillet break test should be run using the proposed welding procedure over the painted surface. zinc. and to identify it. which are usually compatible with welding. however welds are made over paint. and hydrocarbons will be detrimental. is shot blasted. and then stored outdoors. and the paint must be dry. 6-33. The normal paint film thickness should be used. silicon. and are not compatible with welding. every effort should be made to obtain a prime paint that is compatible with welding. if the steel at the point of stress concentration is notch sensitive at the service temperature. Cutting through many layers of lead paint will cause an abnormally high lead concentration in the immediate area and will require special precautions such as extra ventilation or personnel protection. lead. Other paints may contain zinc. The surfaces should be painted with the paint under consideration. or titanium will generally be compatible. (2) There are at least three factors involved with the success of the weld when welding over painted surfaces: the compatibility of the paint with welding. Anything that is a harmful ingredient such as lead. Certain paints contain large amounts of aluminum or titanium dioxide. OTHER WELDING PROBLEMS a. Painting is done to preserve the steel during storage. The paint manufacturer or supplier should be consulted. When this practice is used. vinyls.loading. steel. it is specifically stated that welding should be done on clean metal. It should be broken and the weld examined. Demolition of old structural steel work that had been painted many times with flame-cutting or arc-cutting techniques can create health problems. and the paint film thickness. and other hydrocarbons. In some industries.
. given a coating of prime paint. when it is received from the steel mill.

The paint will also cause porosity if there is sufficient oil present. (2) Postweld treatment for insuring paint film success consists of mechanical and chemical cleaning. as they may react chemically. Other nonferrous metals should be investigated for reactivity prior to cleaning. since it takes a considerable length of time for the hydrocarbons to evaporate. or sand or grit blasting. before welding. Many paints employ an oil base which is a hydrocarbon. If the paint film thicknesses are double that amount. The antispatter compound must be compatible with the paint to be used.
. Sand or grit blasting is the most effective mechanical cleaning method. Some paints may be compatible if the thickness of the film is a maximum of 3 to 4 mm. The metallurgical factors of the weld bead and the smoothness of the weld are of minor importance with regard to the success of the paint. In addition to mechanical cleaning. such as occurs at an overlap area. Preweld treatment found most effective is to use antispatter compounds. CAUTION Aluminum and aluminum alloys should not be cleaned with caustic soda or cleaners having a pH above 10.(5) The dryness of the paint should be considered. power wire brushing. Spatter on or adjacent to the weld leads to rusting of the base material under the paint. (6) The thickness of the paint film is another important factor. Painting over welds is also a problem. These paints dry slowly. Mechanical cleaning methods can consist of hand chipping and wire brushing. The success of any paint film depends on its adherence to the base metal and the weld. chemical bath washing is also recommended. It seems that the paint does not completely adhere to spatter and some spatter does fall off in time. The antispatter compound extends the paint life because of the reduction of spatter. (7) Tests should be run with the dry maximum film thickness to be used with the various types of paints to determine which paint has the least harmful effects on the weld deposit. hydrogen will be in the arc atmosphere and can contribute to underbead cracking. Paint failure occurs when the weld and the immediate area are not properly cleaned prior to painting. which is influenced by surface deposits left on the weld and adjacent to it. there is the possibility of weld porosity. power wire brushing is the next most effective method. leaving bare metal spots in the paint coating. Paint films that are to be welded over should be of the minimum thickness possible. c. If welding is done before the paint is dry. (1) The success of the paint job can be insured by observing both preweld and postweld treatment. Water based paints should also be dry prior to welding. When sand or grit blasting cannot be used. it is prepared for painting. If the weldment is furnace stress relieved and then grit blasted. Slag coverings on weld deposits must be thoroughly removed from the surface of the weld and from the adjacent base metal. Deterioration of the paint over the weld also seems to be dependent upon the amount of spatter present. as well as cleaning the weld area.

mechanically clean the weld and adjacent area. the weld should be scrubbed with water. Weld slag of many electrodes is alkaline in nature and for this reason must be neutralized to avoid chemical reactions with the paint.
. it will be more effective in neutralizing and removing the slag. If water only is used. It must be followed by a water rinse. and wash the weld area with a neutralizing bath and rinse. For this reason. which will usually remove the residual coating slag and smoke film from the weld. which might otherwise occur. (4) Successful paint jobs over welds can be obtained by observing the following: minimize weld spatter using a compatible anti-spatter compound. (3) It has been found that the method of applying paint is not an important factor in determining the life of the paint over welds. If a small amount of phosphoric acid up to a 5% solution is used. The type of paint employed must be suitable for coating metals and for the service intended. which will cause the paint to loosen and deteriorate. it is advisable to add small amounts of phosphate or chromate inhibitors to the water to avoid rusting.Different types of coatings create more or less problems in their removal and also with respect to paint adherence.

b. CHARACTERISTICS
7-1. are pig iron. All these types of iron are mixtures of iron and carbon. and tool steel. Aluminum. after undergoing certain processes. and titanium alloys are among those metals which belong to this group. All metals fall within two categories. Physical Properties.CHAPTER 7 METALS IDENTIFICATION
Section I. 7-2. The various alloys of iron.
. wrought iron. with particular reference to their significance in welding operations. magnesium. Definitions. silicon. (2) Nonferrous metals are those which do not contain iron. malleable cast iron. gray cast iron. copper. Ferrous metals appear in the form of cast iron. Other elements are also present. carbon steel. sulfur. Physical properties of various metals are shown in table 7-1. PROPERTIES OF METALS a. white iron. ferrous or nonferrous. alloy steel. This section describes the characteristics of metals and their alloys. GENERAL Most of the metals and alloys used in Army materiel can be welded by one or more of the processes described in this manual. white cast iron. (1) Ferrous metals are metals that contain iron. and phosphorous. and carbon steel. manganese. Many of the physical properties of metals determine if and how they can be welded and how they will perform in service. but in amounts that do not appreciably affect the characteristics of the metal.

. Color relates to the quality of light reflected from the metal.(1) Color.

is of vital importance in welding. (5) Conductivity. (4) Boiling point. the temperature at which the metal changes from a solid to a molten state. For example. Expansion is the increase in the dimension of a metal caused by heat. will vaporize. This property is particularly important to resistance welding and to electrical circuits. however. This property is measured by grams per cubic millimeter or centimeter in the metric system. As temperature of a metal increases. The boiling point is the temperature at which the metal changes from the liquid state to the vapor state. A measure of electrical conductivity is provided by the ability of a metal to conduct the passage of electrical current. this property is the ratio of the mass of a given volume of the metal to the mass of the same volume of water at a specified temperature. since one metal may transmit heat from the welding area much more quickly than another. there is an absorption of heat during melting and a liberation of heat during freezing. Thermal conductivity. The coefficient of linear thermal expansion is a measure of the linear increase per unit length based on the change in temperature of the metal. Mass or density relates to mass with respect to volume. (3) Melting point. Mercury is the only common metal that is in its molten state at normal room temperature. The expansion of a metal in a longitudinal direction is known as the linear expansion. The absorption or release of thermal energy when a substance changes state is called its latent heat. Boiling point is also an important factor in welding. usually 20°C. (6) Coefficient of linear thermal expansion. During this process. The thermal conductivity of a metal indicates the need for preheating and the size of heat source required. its conductivity decreases. Thermal conductivity is measured in calories per square centimeter per second per degree Celsius. Temperature bears an important part in this property. Thermal and electrical conductivity relate to the metal’s ability to conduct or transfer heat and electricity.(2) Mass or density. Copper has the highest thermal conductivity of the common metals. With few exceptions. The coefficient of linear expansion is expressed as the linear expansion per
. Commonly known as specific gravity. Metals having low melting temperatures can be welded with lower temperature heat sources. A metal’s fusibility is related to its melting point. Pure substances have a sharp melting point and pass from a solid state to a liquid without a change in temperature. solids expand when they are heated and contract when they are cooled. The melting point of a metal is important with regard to welding. Electrical conductivity is usually considered as a percentage and is related to copper or silver. Electrical conductivity is the capacity of metal to conduct an electric current. the ratio of weight of one cubic foot of water to one cubic foot of cast iron is the specific gravity of cast iron. Aluminum has approximately half the thermal conductivity of copper. exceeded only by silver. the ability of a metal to transmit heat throughout its mass. Some metals. Thermal conductivity is usually related to copper. when exposed to the heat of an arc. Its opposite is resistivity. and steels have abut one-tenth the conductivity of copper. which is measured in micro-ohms per cubic centimeter at a standardize temperature. usually 39°F (4°C). The soldering and brazing processes utilize lowtemperature metals to join metals having higher melting temperatures.

moisture. This is important for welding with respect to warpage. hardness. Mechanical properties of various metals are shown in table 7-2. wapage control and fixturing. The most common mechanical properties considered are strength. Mechanical Properties. The adequacy of a weld depends on whether or not it provides properties equal to or exceeding those of the metals being joined. Mechanical properties are also used to help specify and identify the metals. The mechanical properties of metals determine the range of usefulness of the metal and establish the service that can be expected. (7) Corrosion resistance. expanding almost twice as much as steel for the same temperature change. When metals increase in size. They are important in welding because the weld must provide the same mechanical properties as the base metals being joined. The coefficient of linear and volumetric expansion varies over a wide range for different metals. ductility. or the ability of a material to resist being pulled
. or other agents.
(1) Tensile strength. and for welding together dissimilar metals. and impact resistance. they increase not only in length but also in breadth and thickness. Aluminum has the greatest coefficient of expansion. Corrosion resistance is the resistance to eating or wearing away by air.unit length for one degree of temperature increase. Tensile strength is defined as the maximum load in tension a material will withstand before fracturing. c. This is called volumetric expansion.

4 mm) thick (fig. yield strength. elongation.apart by opposing forces.4 mm) wide and 1. Also known as ultimate strength. it is the maximum strength developed in a metal in a tension test.
(3) Fatigue strength. tensile strength. 7-1). Fatigue strength values are used in the design of aircraft wings and other structures subject to rapidly fluctuating loads.00 in.
. or the ability of a metal to resist being fractured by opposing forces not acting in a straight line (fig.) The tensile strength is the value most commonly given for the strength of a material and is given in pounds per square inch (psi) (kiloPascals (kPa)). For example. (The tension test is a method for determining the behavior of a metal under an actual stretch loading. and cold work. yield point. Shear strength is the ability of a material to resist being fractured by opposing forces acting of a straight line but not in the same plane.0 in. (25. As the shaft is rotated. and the reduction in area. a rotating shaft which supports a weight has tensile forces on the top portion of the shaft and compressive forces on the bottom. corrosive environment. This test provides the elastic limit. Fatigue strength is the maximum load a material can withstand without failure during a large number of reversals of load.
(2) Shear strength. 7-2). (25. The tensile strength is the number of pounds of force required to pull apart a bar of material 1. Fatigue strength is influenced by microstructure. there is a repeated cyclic change in tensile and compressive strength. surface condition.

Malleability is another form of plasticity. The ductility of a metal can be determined by the tensile test by determining the percentage of elongation.
. tin. silver. The compressive strength of both cast iron and concrete are greater than their tensile strength. stretched. The yield point is the point at which definite damage occurs with little or no increase in load. (9) Malleability. Compressive strength is the maximum load in compression a material will withstand before a predetermined amount of deformation. 7-3). (7) Ductility. The lack of ductility is brittleness or the lack of showing any permanent damage before the metal cracks or breaks (such as with cast iron). The ductility of a metal is that property which allows it to be stretched or otherwise changed in shape without breaking. and dimensions after being deformed. and is the ability of a material to deform permanently under compression without rupture. The elastic limit is the point at which permanent damage starts. It is the ability of a material. Gold has exceptional malleability and can be rolled into sheets thin enough to transmit light. or pulled out of shape.
(5) Elasticity. Plasticity is the ability of a metal to be deformed extensively without rupture. and lead are examples of metals exhibiting high malleability. Plasticity is similar to ductility. and to retain the changed shape after the load has been removed. Gold. (8) Plasticity. or the ability of a material to withstand pressures acting in a given plane (fig. It is this property which allows the hammering and rolling of metals into thin sheets. The modulus of elasticity is the ratio of the internal stress to the strain produced. Elasticity is the ability of metal to return to its original size.(4) Compressive strength. (6) Modulus of elasticity. (10) Reduction of area. For most materials. to be drawn or stretched permanently without fracture. The yield strength is the number of pounds per square inch (kiloPascals) it takes to produce damage or deformation to the yield point. such as copper. the reverse is true. shape. This is a measure of ductility and is obtained from the tensile test by measuring the original cross-sectional area of a specimen to a cross-sectional area after failure.

(11) Brittleness. (13) Machinability and weldability. It takes a combination of hardness and toughness to withstand heavy pounding. A brittle metal is one than cannot be visibly deformed permanently. plus the ability to resist failure after the damage has begun. Toughness is the ability of a material to resist the start of permanent distortion plus the ability to resist shock or absorb energy. (15) Impact resistance. The property of machinability and weldability is the ease or difficulty with which a material can be machined or welded. Toughness is a combination of high strength and medium ductility. or one that lacks plasticity. (12) Toughness. Brittleness is the property opposite of plasticity or ductility. A metal may possess satisfactory ductility under static loads. It is the ability of a material or metal to resist fracture. slowly or suddenly applied. Resistance of a metal to impacts is evaluated in terms of impact strength. A tough metal. and which will deform before failure. The impact strength of a metal is determined by measuring the energy absorbed in the fracture.
. (14) Abrasion resistance. such as cold chisel. (16) Hardness. since toughness decreases as hardness increases. Abrasion resistance is the resistance to wearing by friction. but may fail under dynamic loads or impact. Hardness is the ability of a metal to resist penetration and wear by another metal or material. Table 7-3 illustrates hardness of various metals. is one that can withstand considerable stress. The hardness of a metal limits the ease with which it can be machined.

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and the Brinell hardness number (bhn) is determined by from standard tables (table 7-3). The diameter of the dent in the surface is then measured. This test measures hardness by letting a diamondtipped hammer fall by its own weight from a fixed height and rebound from the surface. In this test. the rebound is measured on a scale. The same light load is always used.(a) Brinell hardness test. (c) Scleroscope hardness test. It is used on smooth surfaces where dents are not desired. (b) Rockwell hardness test.
. the heavy load is applied. indicate the type of penetrator used and the amount of heavy load (table 7-3). The letter designations on the Rockwell scale. without moving the piece. such as B and C. The hardness number is automatically indicated on a dial. The light load is first applied and then. a hardened steel ball is pressed slowly by a known force against the surface of the metal to be tested. This test is based upon the difference between the depth to which a test point is driven into a metal by a light load and the depth to which it is driven in by a heavy load.

Welders and metal workers must be able to identify various metal products so that proper work methods may be applied. the welder will learn that certain parts of machines or equipment are always cast iron. and table 7-3. and so on. General. other parts are usually forgings. which presents hardness data. They must be examined in order to determine the metal to be used and its heat treatment. These tests are as follows:
.a. There are seven tests that can be performed in the shop to identify metals. After some practice. These should be supplemented by tables 7-1 and 7-2 which present physical and mechanical properties of metal. drawings (MWOs) should be available. For Army equipment. It is necessary to know the composition of the metal being welded in order to produce a successful weld. if required. Six of the different tests are summarized in table 7-4. b. Tests.

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This will be true of copper. magnesium. The oxidation on steel. the oxidation can be scraped off to determine the color of the unoxidized metal. lead. in which case it would be cast iron. such as a casting with its obvious surface appearance and parting mold lines. they may divide into three short lines. (b) The spark resulting from the test should be directed downward and studied. or hot rolled wrought material. The color. shape. Some metal can be quickly identified by looking at the surface of the broken part or by studying the chips produced with a hammer and chisel. it is one of the more ductile metals. Form and shape give definite clues as to the identity of the metal. (3) Spark test. It can distinguish many metals such as copper. is usually a clue that can be used to separate plain carbon steels from the corrosion-resisting steels. magnesium. for example. pipe can be cast. or wrought. it is one of the brittle metals. the coarseness or roughness of the broken surface is an indication of its structure. The straight lines are called carrier lines. since they do not exhibit spark streams of any significance. They are usually solid and continuous. At the end of the carrier line. shape. it is called a sprig. length. yet soft enough to keep a free-cutting edge. and magnesium. The ease of breaking the part is also an indication of its ductility of lack of ductility. Grinding wheels should be hard enough to wear for a reasonable length of time. I beams or angle irons. or forks. or rust. This test does not replace chemical analysis. and activity of the sparks relate to characteristics of the material being tested. Form should be considered and may show how the part was rode. (2) Fracture test. aluminums. brass. If it breaks easily with little or no bending. Sprigs also
.(1) Appearance test. For example. and pipe fittings. However. Color provides a very strong clue in metal identification. The grinding wheel should be run to give a surface speed of at least 5000 ft (1525 m) per minute to get a good spark stream. The spark test is a method of classifying steels and iron according to their composition by observing the sparks formed when the metal is held against a high speed grinding wheel. If the spark stream divides into more lines at the end. the different kinds of iron and steel produce sparks that vary in length. If the piece bends easily without breaking. The shape can be descriptive. pipes. (a) Spark testing is not of much use on nonferrous metals such as coppers. The spark stream has specific items which can be identified. If metals are oxidized. The surface will show the color of the base metal without oxidation. reinforcing rods. and color. The appearance test includes such things as color and appearance of machined as well as unmachined surfaces. aluminum. which would normally be steel. automobile bumpers. This helps to identify lead. since the color of the spark is important. In other cases. and the precious metals. extruded or cold rolled with a smooth surface. it is best to use standard samples of metal for the purpose of comparing their sparks with that of the test sample. In all cases. this is one way to separate ferrous and nonferrous metals. shape includes such things as cast engine blocks. and nickel-base alloys. but is a very convenient and fast method of sorting mixed steels whose spark characteristics are known. When held lightly against a grinding wheel. Spark testing should be done in subdued light. and even copper.

machined forgings or finished parts. Additionally. Wheel pressure against the work is important because increasing pressure will raise the temperature of the spark stream and give the appearance of higher carbon content. and a steel with 1.occur at different places along the carrier line. the welder can identify various metals by studying how fast the metal melts and how the puddle of molten metal and slag looks. a carbon tool steel exhibits pronounced bursting. In some cases. and the reaction of incandescent particles at the end of the spark stream should be observed. The sparks near and around the wheel. they are called spear points or buds. (4) Torch test. continue.00 percent carbon shows brilliant and minute explosions or sparklers.
.48 cm) long and at right angles to the line of vision. whereas low-carbon steels and most alloy steels have relatively long streams. and perhaps enlarge again for a short length. (30. while cast irons are reddish to straw yellow.
CAUTION The torch test should be used with discretion. Cast irons have extremely short streams.15 percent carbon steel shows sparks in long streaks with some tendency to burst with a sparkler effect. as well as color changes during heating. (c) One big advantage of this test is that it can be applied to metal in. Sparks produced by various metals are shown in figure 7-4. bar stock in racks. With the oxyacetylene torch. The spark test is best conducted by holding the steel stationary and touching a high speed portable grinder to the specimen with sufficient pressure to throw a horizontal spark stream about 12. When a sharp corner of a white metal part is heated. as it may damage the part being tested.00 in. all stages. High sulfur creates these thicker spots in carrier lines and the spearheads. As the carbon content increases. Steels usually have white to yellow color sparks. the intensity of bursting increases. magnesium may ignite when heated in the open atmosphere. the middle of the spark stream. A 0. When these heavier portions occur at the end of the carrier line. the carrier line will enlarge slightly for a very short length. These are called either star or fan bursts.

and to the above information on the three hardness tests that are commonly used. iron alloys. Magnesium will burn with a sparkling white flame. such as in a seamless tube. The ease of producing a chip is an indication of the hardness of the metal. the sharp corner will melt quickly. Copper alloys. On such materials as aluminum. annealed 18 chrome 8 nickel stainless. broken fragments. whereas if chips break apart. if composed of lead. (6) Chisel test. zinc-base alloys. the approximate Brinell hardness. it is normally deoxidized copper. aluminum-base alloys. A slightly magnetic reaction is obtained from Monel and high-nickel alloys and the stainless steel of the 18 chrome 8 nickel type when cold worked. A sharp mill file must be used. it is possible to judge a strongly magnetic material from a slightly magnetic material. mild steel and malleable iron. and martensitic stainless steels. In the case of copper. The magnetic test can be quickly performed using a small pocket magnet. the chips are hard to obtain because of the hardness of the material. it is electrolytic copper. since zinc is not a good conductor. It is assumed that the part is steel and the file test will help identify the type of steel. it is indicative of a ductile metal. Refer to table 7-3 for hardness values of the various metals. A less precise hardness test is the file test. Strongly magnetic materials include the carbon and low-alloy steels. and the precious metals. If it does not melt until much heat has been applied. pure nickel. To distinguish aluminum from magnesium. The chips for gray cast iron are so brittle that they become small. if the sharp comer melts. (7) Hardness test. If the part is zinc. Use the cold chisel to hammer on the edge or corner of the material being examined. The chip test or chisel test may also be used to identify metals. (5) Magnetic test. Nonmagnetic materials include copper-base alloys. the chips are continuous. If the chip is continuous. it will not melt until sufficient heat has been used because its high conductivity. The only tools required are a banner and a cold chisel. On high-carbon steel. apply the torch to filings. A summary of the reaction to filing.
. If the material is aluminum. With experience. but can be continuous. the magnesium. and the possible type of steel is shown in table 7-6. Steel will show characteristic colors before melting. will boil. The nonmagnetic materials are easily recognized.the rate of melting can be an indication of its identity. it indicates a brittle material. They are easily chipped and the chips do not tend to break apart.

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. Color Code for Marking Steel Bars. The basic substance used to make both steel and cast iron (gray and malleable) is iron. the two most important oxides being hematite and magnetite. coke. d. It will turn blue-green on Monel. Magnesium can be distinguished from aluminum using silver nitrate. The color markings provided in the code may be applied by painting the ends of bars. while twin colors designate alloy and free-cutting steel. There are numerous chemical tests than can be made in the shop to identify some material. Iron ore is reduced to pig iron in a blast furnace. It is used in the form of pig iron. These tests can become complicated. which will leave a black deposit on magnesium. 75). and limestone. Iron is produced from iron ore that occurs chiefly in nature as an oxide. Raw materials charged into the furnace include iron ore. and the impurities are removed in the form of slag (fig. The pig iron produced is used to manufacture steel or cast iron. and for this reason are not detailed further here. The Bureau of Standards of the United States Department of Commerce has a color code for making steel bars. Ferrous Metal. c. but will show no reaction on Inconel. Monel can be distinguished form Inconel by one drop of nitric acid applied to the surface. A few drops of a 45 percent phosphoric acid will bubble on low-chromium stainless steels. Solid colors usually mean carbon steel.(8) Chemical test. but not on aluminum.

Plain carbon steel consists of iron and carbon.5 percent for cast iron. The carbon content range for steel is 0. and 4. nickel. Carbon is the hardening element.7 percent. Cast iron is nothing more than basic carbon steel with more carbon added.03 to 1. Tougher alloy steel contains other elements such as chromium. and molybdenum. along with silicon.
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during which the oxygen is removed from the iron. 7-6). crucible. and coke in a cupola furnace. Malleable cast iron. such as open-hearth. electric-arc. After melting has been completed. and coke are charged into the top of the furnace. It is then poured into sand or alloy steel molds. which is similar in content to gray cast iron except that malleable iron contains less carbon and silicon. The iron ore. the steel is tapped from the furnace into a ladle and then poured into ingots or patterned molds. The carbon present in hardened steel is in solid solution. Iron ore is smelted with coke and limestone in a blast furnace to remove the oxygen (the process of reduction) and earth foreign matter from it. Cast iron is produced by melting a charge of pig iron. the molten metal in the mold is allowed to become solid and cool to room temperature in open air. The iron melts. and induction. When making gray cast iron castings. White cast iron is annealed for more than 150 hours at temperatures ranging from 1500 to 1700°F (815 to 927°C). The ingots are used to make large rectangular bars.
. together with compounds formed by reaction of the flux with substances present in the ore. This also accounts for the higher mechanical properties of malleable cast iron as compared with gray cast iron. Raw materials charged into the furnace include mixtures of iron ore. which are reduced further by rolling operations. Limestone is used to combined with the earth matter to form a liquid slag. The desirable properties of cast iron are less than those of carbon steel because of the difference in chemical makeup and structure. pig iron. limestone. Bessemer converter. while alloy steel is melted in electric-arc and induction furnaces. Coke is used to supply the carbon needed for the reduction and carburization of the ore. while cast iron contains free carbon known as graphite. while in malleable cast iron the graphite is in nodular (rounded) form. and scrap. is made from white cast iron. The molds are used for castings of any design. In gray cast iron. limestone. floats on the heavier iron liquid. Rapid combustion with a blast of preheated air into the smelter causes a chemical reaction. on the other hand. Each material is then drawn off separately (fig. limestone. and the molten slag consisting of limestone flux and ash from the coke. the graphite is in flake form.Steel is produced in a variety of melting furnaces. Most carbon steel is made in open-hearth furnaces. The result is a product called malleable cast iron.

Table 7-7 shows this principle. and wrought iron consist of a mixture of iron. and other elements in small amounts.All forms of cast iron. steel. carbon. Whether the metal is cast iron or steel depends entirely upon the amount of carbon in it.
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tensile strength of 35.plated. (d) Limitations. and are the reason why cast iron is brittle. (1) Wrought iron. machined. Wrought iron can be gas and arc welded. The appearance of wrought iron is the same as that of rolled. and is ductile and corrosion resistant. In the process of manufacture. low-carbon steel. farm implements. which cause rusting. and malleable cast iron are all produced from a similar base. Carbon and other elements present in pig iron are taken out. causing most of the remaining carbon to separate.08 percent. modern household furniture. (f) Appearance test. white. It is made from pig iron in a puddling furnace and has a carbon content of less than 0.Cast iron differs from steel mainly because its excess of carbon (more than 1.000 psi.
. Thus. melting point of 2750°F (1510°C). some slag is mixed with iron to form a fibrous structure in which long stringers of slag. By carefully controlling the silicon content and the rate of cooling. Wrought iron has low hardness and low fatigue strength. Because of the presence of slag. These particles of graphite form the paths through which failures occur. nails. leaving almost pure iron.7 percent) is distributed throughout as flakes of graphite. (b) Uses. (a) General. chains. barbed wire. running lengthwise. fencing. wrought iron resists corrosion and oxidation. and decorations. (e) Properties. it is possible to cause any definite amount of the carbon to separate as graphite or to remain combined. and is easily formed. are mixed with long threads of iron. specific gravity of 7. Wrought iron is almost pure iron. gray.7. (c) Capabilities. Wrought iron is used for porch railings. Wrought iron has Brinell hardness number of 105.

As a result. and the metal is shot throughout with tiny.75 to 1. hardened.375 to 344. Cast iron has a Brinell hardness number of 150 to 220 (no alloys) and 300 to 600 (alloyed).000 to 50.(g) Fracture test. good wear resistance. it acts like rolled steel. Total carbon content is between 1.
.50 to 4. Much of the carbon separates as tiny flakes of graphite scattered throughout the metal. (2) Cast iron (gray. The metal is soft and easily cut with a chisel. Wrought iron has a fibrous structure due to threads of slag.75 percent remains in the free or graphitic state. (b) Uses. etc. transmission housing. Commercial gray iron has 2. A portion of the carbon exists as free carbon or graphite. (f) Gray cast iron. and change to white.50 percent nickel and 0. while about 2. and fair corrosion resistance. (h) Spark test. It has a peculiar slag coating with white lines that are oily or greasy in appearance. Wrought iron melts quietly without sparking. carbon. and silicon. Cast iron may be brazed or bronze welded. pistons.5 percent. machine tool castings. When wrought iron is ground. (a) General. engine blocks. Since graphite is an excellent lubricant.000 psi (344. Cast iron is a manmade alloy of iron. causes the gray appearance of the fracture. it can be split in the direction in which the fibers run. which characterizes ordinary gray cast iron. However.500 kPa) (alloyed). flaky cleavages. (e) Properties. and silicon. as distinguish from combined carbon.50 percent chromium or 0. high compressive strength that is four times its tensile strength.7 and 4. and is quite ductile. gas and arc welded. and malleable). straw-colored sparks form near the grinding wheel. (i) Torch test. specific gravity of 7.50 percent carbon. the chemical compound of iron and carbon breaks up to a certain extent. Wrought iron cannot be hardened. or machined. the break is very jagged due to its fibrous structure. (d) Limitations. This graphitelike carbon. gray cast iron is easy to machine but cannot withstand a heavy shock.000 psi (172. About 1 percent of the carbon is combined with the iron. It cannot be worked cold. forked sparklers near the end of the stream. high rigidity. In making gray cast iron. tensile strength of 25. Special high-strength grades of this metal also contain 0. (c) Capabilities. If the molten pig iron is permitted to cool slowly. white. When nicked and bent.6. phosphorus. Cast iron is used for water pipes.750 kPa) (no alloys) and 50. Cast iron must be preheated prior to welding.750 to 689.000 to 100.25 to 1.25 percent molybdenum. manganese. stove castings. sulfur.25 to 0. Gray cast iron consists of 90 to 94 percent metallic iron with a mixture of carbon.

Any welded part should be annealed after welding. repeated spurts that change to a straw color. In general.the silicon content is usually increased. which is a small percentage of the total carbon present in cast iron. This free carbon separates in a different way from carbon in gray cast iron and is called temper carbon. Nick a corner all around with a chisel or hacksaw and strike the corner with a sharp blow of the hammer. 3. tough film forms on the surface as it melts.5 percent by weight. the more free carbon (graphitic carbon) present in cast iron. ductility. A small volume of dull-red sparks that follow a straight line close to the wheel are given off when this metal is spark tested. Fracture test. It exists in the form of small. Small. Unmachined castings may be ground in places to remove rough edges. The castings have properties more like those of pure iron: high strength. The torch test results in a puddle of molten metal that is quiet and has a jelly like consistency. When gray cast iron is heated to the molten state. 1. When the torch flame is raised. and is referred to as combined carbon. Appearance test. These break up into many fine. and white cast iron is formed. The carbon in this type of iron measures above 2. probably combining chemically with it. brittle chips made with a chisel break off as soon as they are formed. A heavy. The unmachined surface of gray cast iron castings is a very dull gray in color and may be somewhat roughened by the sand mold used in casting the part. 4. Malleable cast iron is made by heating white cast iron from 1400 to 1700°F (760 and 927°C) for abut 150 hours in boxes containing hematite ore or iron scale. the lower the combined carbon content and the softer the iron. Cast iron castings are rarely machined all over. (g) White cast iron. often impossible to machine. is known as cementite. since this allows the formation of graphitic carbon. (h) Malleable cast iron. Torch test.5 to 4. The combined carbon (iron carbide). Cast iron breaks short when fractured. Malleable cast iron can be welded and brazed. the depression in the surface of the molts-puddle disappears instantly.
. If this molten metal is cooled quickly. This heating causes a part of the combined carbon to change into the free or uncombined state. the carbon completely dissolves in the iron. rounded particles of carbon which give malleable iron castings the ability to bend before breaking and to withstand shock better than gray cast iron. The dark gray color of the broken surface is caused by fine black specks of carbon present in the form of graphite. The molten puddle takes time to harden and gives off no sparks. the two elements remain in the combined state. White cast iron is very hard and brittle. and ability to resist shock. and has a silvery white fracture. Spark test. toughness. 2.

It is dull gray and somewhat lighter in color than gray cast iron. they are somewhat longer and are present in large volume. After the flame has been withdrawn. depending on the type of steel. When malleable cast iron is fractured. and a melting point of 2800° F (1538°C). When malleable cast iron is ground. A form of iron. steel-like band gives off sparks. 99.250 kPa) for alloyed steel.1. 80. chisels. (b) Uses. As the interior is reached. Highly alloyed steel is difficult to produce. structural steel. (f) Low-carbon steel (carbon content up to 0. roles.034. Spark test. all to varying degrees. but considerably more than wrought iron. and forged. This steel is soft and ductile. the outer. When of good quality. welded. (a) General. rivets. 4. Steel can be machined. steel-like band at the edges. (3) Steel. 2. the central portion of the broken surface is dark gray with a bright. Steel is used to make nails. to increase certain physical properties of the metal. however. the sparks quickly change to a dull-red color near the wheel. the melted parts are very hard and brittle. having the appearance of white cast iron (they have been changed to white or chilled iron by melting and fairly rapid cooling). The outside. such as chromium and nickel. hoods. (d) Limitations.000 psi (310.
. gears. but is generally free from sand. sheared. The appearance of the fracture may best be described as a picture frame.600 kPa) for medium-carbon steel. bright. punched. The carbon content is from 0.000 psi (1.30 percent. bright layer gives off bright sparks like steel.03 to 1. When fractured. etc. but the center does not. the surface will be full of blowholes. (e) Properties.000 psi (551. and can be rolled. Appearance test. hammers. 3. desks. Steel has tensile strength of 45. Fracture test. (c) Capabilities. The surface of malleable cast iron is very much like gray cast iron. and 150. These sparks from the interior section are very much like those of cast iron.275 kPa) for lowcarbon steel.000 psi (692. and worked when either hot or cold. Torch test.605 kPa) for high-carbon steel.7 percent. fenders. malleable cast iron is much tougher than other cast iron and does not break short when nicked. Molten malleable cast iron boils under the torch flame. Basic carbon steels are alloyed with other elements. steel contains less carbon than cast iron.

It is tough to chip or nick. dies. Appearance test. Appearance test. and in the annealed or normalized condition in order to be suitable for machining before heat treatment. hammer marks. and other machine tools and hand tools that are heat treated after fabrication to develop the hard structure necessary to withstand high shear stress and wear. 3. This steel is difficult to weld because of the hardening effect of heat at the welded joint. wrought iron.50 percent). except where it has been machined. sheet. This steel may be heat-treated after fabrication. and hardens almost instantly. the weld zone will become hardened if cooled rapidly and must be stress-relieved after welding. and steel castings cannot be hardened. (g) Medium-carbon steel (carbon content ranging from 0. Spark test. The steel gives off sparks in long yellow-orange streaks. 4. the color is bright crystalline gray. It is used for general machining and forging of parts that require surface hardness and strength. brighter than cast iron. whiter than low-carbon steel.
.90 percent).30 to 0. Fracture test. The steel gives off sparks when melted. High-carbon steel gives off a large volume of bright yelloworange sparks. The appearance of the steel depends upon the method of preparation rather than upon composition. and wire forms. This steel is used for the manufacture of drills. 3. springs. however. When low-carbon steel is fractured.50 to 0. Spark test. and is usually worked to produce a smooth surface finish. It is made in bar form in the cold-rolled or the normalized and annealed condition. or fins. 1. It does not harden to any great amount. High-carbon steel can be hardened by heating to a good red and quenching in water. forked sparklers. Rolled steel has fine surface lines running in one direction. taps. It is more expensive. (h) High-carbon steel (carbon content ranging from 0. Low carbon steel. During welding. Torch test. 2. Cast steel has a relatively rough. dark-gray surface. that show some tendency to burst into white. 1. it can easily be case hardened.It is easily machined and can readily be welded by all methods. Forged steel is usually recognizable by its shape. It is manufactured in bar. The unfinished surface of high-carbon steel is dark gray and similar to other steel. 2. Tool steel is harder and more brittle than plate steel or other low-carbon material. High-carbon steel usually produces a very fine-grained fracture. Fracture test.

and the melting surface has a porous appearance. Tool steel (carbon content ranging from 0. bubble-like depressions. Where the surface of drop forgings has not been finished. (i) High carbon tool steel. Steel castings are tougher than malleable iron. cutters. Torch test. Alloy steel forgings are harder and more brittle than low carbon steels. (5) Steel forgings. Those containing chromium or vanadium are more difficult to weld. It sparks more freely than low-carbon (mild) steels.55 percent) is used in the manufacture of chisels. The color of a fracture in cast steel is bright crystalline gray. Manganese steel. or both of these metals. When melted. The sparks created from cast steel are much brighter than those from cast iron. and chips made with a chisel curl up more. are easily welded if the carbon content is low. (a) General.20 percent silicon. large taps. (c) Fracture test. and similar parts where high hardness is required to maintain a sharp cutting edge.4. Since manganese steel is nearly always used in the form of castings. This steel is tough and does not break short. unless they have been purposely cleaned. (b) Appearance test. It is difficult to weld due to the high carbon content. is so tough that is cannot be cut with a chisel nor can it be machined. and the sparks are whiter. however. Molten high-carbon steel is brighter than lowcarbon steel. Welding is difficult on steel castings containing over 0. (a) General. This fin is removed by the trimming dies.
. cast steel sparks and hardens quickly. repeating bursts. (4) Cast steel. Steel forgings may be of carbon or alloy steels. razors. All forgings are covered with reddish brown or black scale. shear blades. Alloy steel castings containing nickel. The surface of cast steel is brighter than cast or malleable iron and sometimes contains small. it is also considered with cast steel.30 percent carbon and 0. (d) Spark test. throwing off brilliant sparklers at right angles to the original-path of the spark: (e) Torch test. Its high resistance to wear is its most valuable property. (b) Appearance test. blacksmith’s tools. Manganese steel gives off marks that explode. but enough of the sheared surface remains for identification.90 to 1. A spark test shows a moderately large volume of white sparks having many fine. molybdenum. there will be evidence of the fin that results from the metal squeezing out between the two forging dies. wood-turning tools. The surface of steel forgings is smooth.

Above 0. Chromium is used as an alloying element in carbon steels to increase hardenability. Steel forgings spark when melted. The sparks given off are long. and a given strength is secured with less material weight. yellow-orange streamers and are typical steel sparks. the impact fatigue property is impaired. Sparks from high-carbon steel (machinery and tool steel) are much brighter than those from low-carbon steel. (e) Torch test. Molybdenum is sometimes combined with chromium. or vanadium to obtain desired properties. Tool steel is harder and more brittle than plate steel or other low-carbon material.(c) Fracture test. wrought iron. strength. The fracture is usually whiter and finer grained. molybdenum. Nickel. (d) Spark test. wear resistance. and silicon are the most common elements used in alloy steel. which is the depth of hardening possible through heat treatment. Tool steel can be hardened by heating to a good red and then quenching in water. it is harder to break than cast steel and has a finer grain. and lowers the hardening temperatures so than an oil quench. is used for hardening. above). Alloy steel is frequently recognizable by its use. 4. Wear resistance is improved with molybdenum content above 0. tungsten. 2. 3. They have greater strength and durability than carbon steel. vanadium. (6) Alloy steel. and forging. and ductility of steels.
. It imparts high strength with little loss in ductility. and shock resistance. 1. Molybdenum increases hardenability. Manganese steel is a special alloy steel that is always used in the cast condition (see cast steel. An increase in manganese content decreases the weldability of steel. tungsten. There are many varieties of alloy steel used in the manufacture of Army equipment.60 percent molybdenum. chromium. (a) General. Chips are tough. and the sparks increase in number and brightness as the carbon content becomes greater.75 percent. corrosion resistance. easier hot rolling. The impact fatigue property of the steel is improved with up to 0. Low-carbon steel. Nickel increases the toughness. Manganese is used in steel to produce greater toughness.60 percent molybdenum. The color of a fracture in a steel forging varies from bright crystalline to silky gray. rather than a water quench. and when a sample is nicked. and steel castings cannot be usefully hardened. Forgings may be of low-or high-carbon steel or of alloy steel.

and in combination with other alloys. Titanium and columbium (niobium) are used as additional alloying agents in low-carbon content. Silicon is added to steel to obtain greater hardenability and corrosion resistance. depending upon size and shape. High yield strength.000 psi (689.000 to 100. these steels are more corrosion and abrasion resistant. (d) Spark test. Structural members fabricated of these high strength steels may have smaller cross sectional areas than common structural steels. and still have equal strength. corrosion resistant steels. (b) Appearance test.300 kPa). this alloy appears very similar to the low carbon steels. 9.500 kPa) and a tensile strength of 100.5. 6. 8. These steels are quenched and tempered to obtain a yield strength of 90. Alloy steel is usually very close grained. The carbon content ranges from 0. dense grain when used in small quantities. It is also added to steel during manufacture to remove oxygen. and is often used with manganese to obtain a strong.550 to 689. Vanadium is used to help control grain size.000 psi (620. They are difficult to weld except by the furnace induction method. tough steel. at times the fracture appears velvety. (c) Fracture test. produces a fine. yet resists tempering. In a spark test. low alloy structural steels (often referred to as constructional alloy steels) are special low carbon steels containing specific small amounts of alloying elements. NOTE This type of steel is much tougher than low carbon steels. it produces a steel that retains its hardness at high temperatures. Alloy steel produces characteristic sparks both in color and shape. 7. Alloy steel appear the same as drop-forged steel. It tends to increase hardenability and causes marked secondary hardness. High speed tool steels are usually special alloy compositions designed for cutting tools.70 to 0. Some of the more common alloys used in steel and their effects on the spark stream are as follows:
. Tungsten. They support resistance to intergranular corrosion after the metal is subjected to high temperatures for a prolonged time period. When used in larger quantities.80 percent.500 to 965. from 17 to 20 percent. as an alloying element in tool steel. In addition. and shearing machines must have twice the capacity required for low carbon steels.000 to 140.

E. In the amounts found in S. Nickel. but onethird as long. 3. Steel containing 14 percent chromium and no nickel produces a shorter version of the lowcarbon spark. High chromium-nickel alloy (stainless) steels. It can be seen even in fairly strong carbon bursts. 7. chromium. there is enough difference in their color to tell them from a tungsten spark. Molybdenum with other elements. 8 percent nickel stainless steel produces a spark similar to that of wrought iron. 6. depending on the other elements present. orange spear points at the end of the carrier lines. 2 percent carbon steel (chromium die steel) produces a spark similar to that of carbon tool steel. Steel containing more than the normal amount of manganese will spark in a manner similar to high-carbon steel with low manganese content. Tungsten. It also shortens the spark stream. 2. Chromium. Carrier lines may be anything from dull red to orange in color. An 18 percent chromium.
. but only half as long. or both. Steel containing 10 percent tungsten causes short. sharply defined dash of brilliant light just before the fork. Tungsten will impart a dull red color to the spark stream near the wheel. 5. Chromium in large amounts shortens the spark stream length to one-half that of the same steel without chromium. but does not appreciably affect the stream’s brightness. Steel containing this element produces a characteristic spark with a detached arrowhead similar to that of wrought iron. or completely eliminates the carbon burst. Other elements shorten the stream to the same extent and also make it duller. the spark stream turns orange. Still lower tungsten content causes small white bursts to appear at the end of the spear point. A moderate increase in manganese increases the volume of the spark stream and the force of the bursts. Molybdenum alloy steel contains nickel.1. steels. Although other elements give off a red spark. curved. There is a medium volume of streaks having a moderate number of forked bursts. 4. Steels containing 1 to 2 percent chromium have no outstanding features in the spark test. The nickel spark has a short. An 18 percent chromium. The sparks given off during a spark test are straw colored near the grinding wheel and white near the end of the streak. A. nickel can be recognized only when the carbon content is so low that the bursts are not too noticeable. When molybdenum and other elements are substituted for some of the tungsten in high-speed steel. Manganese. Steel containing this element produces a spark similar to a carbon steel spark. Molybdenum. if the tungsten content is not too high. decreases the size.

25 percent carbon. are better suited to welding than those with a maximum carbon content of 0.370 to 110.125 kPa). Alloy steels containing vanadium produce sparks with a detached arrowhead at the end of the carrier line similar to those arising from molybdenum steels. High speed tool steels. and a melting point of 1220°F (660°C).30 percent. Electric arc welding with a covered electrode may require preheating of the metal. It is suitable only in low temperature applications.000 psi (41. (1) Aluminum (Al). Nonferrous metal. Aluminum should be used in low-temperature applications. (a) General. In using nickel plate steel. A spark test in these steels will impart a few long. Pure aluminum has a Brinell hardness number of 17 to 27. Aluminum alloys have a Brinell hardness number of 100 to 130. and straw-colored near the end of the spark stream. Aluminum is used as a deoxidizer and alloying agent in the manufacture of steel. and welded. low strength metal which can easily be cast. followed by a proper stressrelieving heat treatment (post heating).7. forged. it has been found that commercial grades of low-alloy structural steel of not over 0. tensile strength of 6000 to 16. aircraft structures. machined. forked sparks which are red near the wheel.000 to 75. e. Vanadium. railways cars. formed. aluminum and aluminum alloys have excellent heat
. is an example of this kind of plate. and transmission lines are made of aluminum. pistons. to produce a structure in which the welded joint has properties equal to those of the plate metal. Castings. 9. formed. soft. Armorplate. specific gravity of 2. (d) Limitations. The spark test is not positive for vanadium steels. a low carbon alloyed steel. Direct metal contact of aluminum with copper and copper alloys should be avoided. wrought alloys and cast alloys. Such plate is normally used in the "as rolled" condition. and tensile strength of 30. (b) Uses.000 psi (206. Plate steel is used in the manufacture of built-up welded structures such as gun carriages. and welded. Aluminum is a lightweight.320 kPa). forged.850 to 517. except when alloyed with specific elements. Commercial aluminum alloys are classified into two groups. (e) Properties. (7) Special steel. (c) Capabilities. kitchen utensils. Aluminum can be cast. and several containing no nickel at all. Generally. torque converter pump housings. The wrought alloy group includes those alloys which are designed for mill products whose final physical forms are obtained by working the metal mechanically. The casting alloy group includes those alloys whose final shapes are obtained by allowing the molten metal to solidify in a mold. machined.8.

silicon. Brinell hardness number of 110 to 170.19. and cobalt. (d) Limitations. high electrical conductivity (60 percent that of copper. copper. forged. volume for volume. machined. and unfairly corrosion resistant. (i) Torch test. can be welded. Aluminum does not turn red before melting. Chromium alloys can be welded.conductivity. Chromium is never used in its pure state. heat. or manganese. It holds its shape until almost molten.
. and is widely used in electroplating. It is also used in electroplating for appearance and wear. The silver nitrate will not react with the aluminum. No sparks are given off from aluminum. and is wear. dull when oxidized. machined. Aluminum strongly resembles magnesium in appearance. It is hard. Castings are alloys of aluminum with other metals. Aluminum is light gray to silver in color. A heavy film of white oxide forms instantly on the molten surface. magnesium.25 to 0. (h) Spark test. Wrought aluminum alloys may contain chromium. (c) Capabilities. silicon. Chromium is not resistant to hydrochloric acid. bright structure. and to make mirrors and stainless steel. aluminum. usually zinc. high strength/weight ratio at room temperature. very bright when polished. copper.35 percent) and in nonferrous alloys of nickel. A fracture in an aluminum casting shins a bright crystalline structure. (e) Properties (pure). Chromium is an alloying agent used in steel. then collapses (hot shorts) suddenly. corrosion resistant. is resistant to acids other than hydrochloric. in powder metallurgy. (f) Appearance test. and corrosion resistant. Chromium has a specific gravity of 7. Rolled and sheet aluminum materials are usually pure metal. Aluminum is distinguished from magnesium by the application of a drop of silver nitrate solution on each surface. Chromium is one of the most widely used alloys. and light in weight. copper. (b) Uses. and nonferrous alloys of nickel. aluminum. (a) General. (2) Chromium (Cr). and cannot be used in the pure state because of its brittleness and difficulty to work. Chromium is not resistant to hydrochloric acid and cannot be used in its pure state because of its difficulty to work. brittle. and cobalt. cast iron. and sometimes iron and magnesium. and forged. It is used as an alloying agent in steel and cast iron (0. (g) Fracture test. a melting point of 3300°F (1816°C). A fracture in rolled aluminum sections shows a smooth. but leaves a black deposit of silver on the magnesium.

high-speed tool bits and cutters. In the metallic form. specific gravity of 8. and Monel metal. Cobalt alloy (Stellite 21) has a tensile strength of 101. Cobalt must be machined with cemented carbide cutters.000 psi (696. but has a slightly bluish cast. cobalt does not have many uses.430 kPa). Nickel is added to copper zinc alloys (brasses) to lighten their color. Cobalt is mainly used as an alloying element in permanent and soft magnetic materials. and cutters. Gas welding is the preferred process for joining copper and copper alloys. machined (limited). but loses ductility and gains tensile strength when hardened. the other containing 55 to 60 percent copper and nickel combined. Nickel copper contains either 10.395 kPa) and is heat and corrosion resistant. stress corrosion. Brinell hardness number of 125. bits. (c) Capabilities. Though it is very soft.75 percent beryllium. Pure cobalt has a tensile strength of 34. when combined with other elements. bronze. (4) Copper (Cu). and spinning. The first type can be cold worked by such operations as deep drawing. (d) Limitations. it is used for hard facing materials. Beryllium copper contains from 1. Cobalt is a hard. one type containing 65 percent or more copper and nickel combined. the resultant alloys are called nickel silver. and has high electrical and heat conductivity. it is very difficult to machine due to its high ductility. which increases with the nickel content. (b) Uses. However. Welding high carbon cobalt steel often causes cracking. Copper is a reddish metal. It is also used in the manufacture of nonferrous alloys such as brass. Typical
. and corrosion fatigue. The second type is much harder end is not processed by any of the cold working methods. is very ductile and malleable. or 30 percent nickel. and cemented carbide tools. white metal similar to nickel in appearance. quite tough. and a melting point of 2720°F (1493°C). (b) Uses.50 to 2. creepresisting alloys. and ductile. high-temperature. Nickel alloys have moderately high to high tensile strength.(3) Cobalt (Co). and cold-drawn. These alloys are of two general types. Cobalt can be welded. It is used as a major element in hundreds of alloys. (e) Properties. 20. They are moderately hard. (a) General. Commercially pure copper is not suitable for welding.000 psi (234. They are very resistant to the erosive and corrosive effects of high velocity sea water. (a) General. It is ductile when soft. The principal use of commercially pure copper is in the electrical industry where it is made into wire or other such conductors.9. stamping. It is also used in making insoluble paint pigmnts and blue ceramic glazes.

nickel. (g) Fracture test. and cold worked.700 kPa). an alloy of copper and zinc (60 to 68 percent copper and 32 to 40 percent zinc). which is free from crystalline appearance. They oxidize to various shades of green. has a Brinell hardness number of 60 to 110.9.copper products are sheet roofing. has good machinability. brown. (e) Properties. or yellow. Copper alloys can be welded. manganese. All differ in copper and zinc content. a larger flame is required to produce fusion of copper than is needed for the same size piece of steel. rolled.000 to 60. and can be welded. melting point of 1980°F (1082°C). a tensile strength of 32. but its machinability is only fair. or forged. (i) Torch test. red. The color of polished brass and bronze varies with the composition from red. (j) Brass and bronze. cast. Pure copper is nonmagnetic. to yellow brass. zinc. (f) Appearance test. wire. bearings.640 to 413.000 psi (220. or phosphorus. Pure copper is not suitable for welding and is difficult to machine due to its ductility. e. yellow.
. have good machinability.. i. There are several types of brass. cartridge cases. cast. 1. and commercial. Brass. tin. depending upon composition and method of preparation. and is corrosion resistant. almost like copper. Copper melts suddenly and solidifies instantly. Copper is red in color when polished. and statues. containing small amounts of other metals. It has high strength. Because copper conducts heat rapidly. and oxidizes to various shades of green. specific gravity of 8. (c) Capababilities. The surface of fractured brass or bronze ranges from smooth to crystalline. Bronze is an alloy of copper and tin and may contain lead. bushings. (d) Limitations. (h) Spark test. Copper presents a smooth surface when fractured. Appearance test. or iron.550 kPa) and a Brinell hardness number of 100 to 185. Copper alloys have a tensile strength of 50. 2. Electrolytic tough pitch copper cannot be welded satisfactorily. Copper alloy.000 psi (344. Copper can be forged. It can also be welded.000 to 90. Fracture test. manganese. Copper gives off no sparks. admiralty. melts more easily and solidifies more slowly than pure copper. and can be welded.750 to 620. has a low melting point and high heat conductivity. is rust or corrosion resistant. may be alloyed with other elements such as lead. such as naval.

Spark test. welded. Aluminum bronze presents a smooth surface when fractured. Lead is also used for X-ray protection (radiation shields). moisture. which gives off white fumes when it is melted. and low creep strength. and machined. CAUTION Lead dust and fumes are poisonous. malleable metal with low melting point. seals. Bronze contains tin. low tensile strength. and use personal protective equipment as described in chapter 2. The low melting point of lead makes the correct welding rod selection very important. Lead is well suited for cold working and casting. Torch test. aluminum bronze appears a darker yellow than brass. Many types of chemical compounds are produced from lead. and shot. (c) Capabilities. Torch test. Brass contains zinc. moisture. When polished. Welding aluminum bronze is very difficult. Exercise extreme care when welding lead. It is corrosion. Lead is used mainly in the manufacture of electrical equipment such as lead-coated power and telephone cables. among these are lead carbonate (paint pigment) and tetraethyl lead (antiknock gasoline). cold worked. 3. Brass and bronze give off no sparks. atmosphere. 4. Lead has more fields of application than any other metal.3. (a) General. It is also used in building construction in both pipe and sheet form. Fracture test. (b) Uses. 1. The surface is quickly covered with a heavy scum that tends to mix with the metal and is difficult to remove. and storage batteries. and is effective against many acids. Even a slight amount of tin makes the alloy flow very freely. and water resistant. Zinc alloys are used in the manufacture of lead weights. and is resistant to many acids. Lead is a heavy. Due to the small amount of zinc or tin that is usually present.
. and in solder. It is resistant to corrosion from ordering atmosphere. but never as much as brass. Spark test. bronze may fume slightly. soft. Appearance test. (5) Lead (Pb). Aluminum bronze gives off no sparks. and water. 4. bearings. 2. bullets. (k) Aluminum bronze. Lead can be cast. like water. gaskets.

Magnesium resembles aluminum in appearance. lead has low electrical conductivity. blowers. It is also used in the manufacture and use of fireworks for railroad flares and signals. and oils. (b) Uses. has a low melting point. chromic and hydrofluoric acids. is white in color. Because of its light weight. Magnesium is moderately resistant to atmospheric exposure. Welding by either the arc or gas process requires the use of a gaseous shield.685 kPa). Magnesium alloy materials are used in sewing machines. specific gravity of 1. Lead has low strength with heavy weight. and tensile strength of 42. and certain parts of the fuselage of aircraft. particularly in the aircraft industry. Magnesium is an extremely light metal.(d) Limitations. Magnesium is used as a deoxidizer for brass. and sand.000 psi (289. Pure magnesium has tensile strength of 12. The polished surface is silver-white. excellent machinability. cast. Like aluminum. It has a very low kindling point and is not very weldable. Pure lead has tensile strength of 2500 to 3000 psi (17. hydrocarbons. landing wheels. (c) Capabilities. and silver.3. and a melting point of 1202°F (650°C).000 psi (82. and is corrosion resistant. is malleable. It is nonmagnetic. and textile machines. it is used in many weight-saving applications. Lead dust and fumes are very poisonous. esters.991 kPa). nickel. and is weldable. and machined.000 psi (220. phenols. Alloy lead B32-467 has tensile strength of 5800 psi (39. and for military purposes. Brinell hardness number of 30 (cast) and 50 (rolled). but quickly oxidizes to a grayish film.000 psi (255. (e) Properties.640 kPa) (forged).237. and most alcohols. Generally. Galvanic corrosion is an important factor in any assembly with magnesium.590 kPa) (hard) and 32. Magnesium is distinguished from aluminum by the use of a silver nitrate solution. The flame can be mothered with suitable materials such as carbon dioxide (CO2). welded. (e) Properties. (a) General. Magnesium in fine chip form will ignite at low temperatures (800 to 1200°F (427 to 649°C)). Magnesium can be forged. foam. (f) Appearance test. (d) Limitations. is self-lubricating.740 kPa) (cast) and tensile strength of 37.115 kPa) (rolled). specific gravity of 11. and a melting point of 620°F (327°C). The solution
.7. except when it is alloyed with manganese and aluminum. Magnesium alloy has Brinell hardness number of 72 (hard) and 50 (forged). hose pieces. many chemicals such as alkalies. but is lighter in weight than aluminum. it is highly corrosion resistant and has a good strength-to-weight ratio. typewriters. bronze. Magnesium castings are used for engine housings. (6) Magnesium (Mg).5 to 20.

Manganese alloy has a tensile strength of 110. (7) Manganese (Mn). and rock crushers.does not react with aluminum. No sparks are given off.000 psi (758. (h) Spark test. It has excellent machinability. but leaves a black deposit of silver on magnesium. percentages of 1 to 15 percent manganese will increase the toughness and the hardenability of the metal involved.440 kPa) (quenched) Brinell hardness number of 330. magnesium should be melted in an atmosphere of inert gas.43: a melting point of 2270°F (1243°C). (8) Molybdenum (Mo). specific gravity of 7. (e) Properties. Magnesium oxidizes rapidly when heated in open air. (a) General. Manganese can be welded. Pure manganese has tensile strength of 72. manganese is highly polishable and brittle. (c) Capabilities. Medium-carbon manganese steels are used to make car axles and gears. Austenitic manganese steels are used for railroad track work. machined. Austenitic manganese steels are best machined with cemented carbide. Magnesium is produced in large quantities from sea water. and is brittle.450 kPa).
. Manganese is used mainly as an alloying agent in making steel to increase tensile strength.000 psi (496. Pure manganese has a relatively high tensile strength. producing an oxide film which is insoluble in the liquid metal. power shovel buckets. (g) Fracture test. and high-speed steel cutters. It is also added during the steel-making process to remove sulfur as a slag. (b) Uses. Magnesium has a rough surface with a fine grain structure. CAUTION Magnesium may ignite and burn when heated in the open atmosphere. As a safety precaution. A fire may result when magnesium is heated in the open atmosphere. but special care must be used when machining because of its low kindling point. (i) Torch test. cobalt. and cold-worked. Manganese is used as an alloying agent in steel to deoxidize and desulfurize the metal. Generally. but is very brittle. In metals other than steel. (d) Limitations.

and resistance to heat. electrical resistance heating elements. welding electrodes. drawn. or machined. (d) Limitations. it will increase ductility.2. lowers the critical point for heat treatment. Monelforged nickel has tensile strength of 100. and easily formed. Nickel alloys have Brinell hardness number of 140 to 230. and high strength and toughness at high temperatures. (b) Uses. specific gravity of 10. specific gravity of 8. Pure molybdenum has a tensile strength of 100. or butt welded by resistance heating in vacuum. aids fatigue strength. (b) Uses. (c) Capabilities.170 kPa).500 kPa). and melting point of 2650°F (1454°C).(a) General. and is corrosion resistant. ornamental trim. Pure nickel has a grayish white color.
. hardenability. Molybdenum is used mainly as an alloy. Pure nickel has tensile strength of 46. rolled. Molybdenum can be swaged. ductile metal. has no effect on grain size. switches. (f) Appearance. Chemical and food processing equipment.500 kPa) (sheet) and 30. (d) Limitations. and hot hydrochloric acid. As an alloy. (a) General.000 Psi (206.9. It is principally used as an alloying agent in steel to increase strength. meting point of 4800°F (2649°C). Nickel alloys are readily welded by either the gas or arc methods. Brinell hardness number of 160 to 185.000 psi (689. Nickel is used in making alloys of both ferrous and nonferrous metal. Pure molybdenum has a high tensile strength and is very resistant to heat. malleable. Molybdenum can only be welded by atomic hydrogen arc. thermocouplers.000 psi (689. Heating elements. (9) Nickel (Ni). contacts. Nickel is a hard. Both nickel and nickel alloys are machinable and are readily welded by gas and arc methods. (e) Properties. It is attacked by nitric acid. cast. Nickel alloys can be machined. and increases impact values in low temperature operations.850 kPa) (wire). (c) Capabilities. it is used in the making of stainless steel. retains hardness and strength at high temperatures. forged. and cathode ray tubes are made of molybdenum. and parts that must withstand elevated temperatures are all produced from nickel-containing metal. hot sulfuric acid. Brinell hardness number 220. (e) Properties.000 psi (317. Nickel oxidizes very slowly in the presence of moisture or corrosive gases. Alloyed with chromium.

Monel metal is a nickel alloy of silver-white color containing about 67. (i) Torch test. orange streaks which are generally wavy. The fracture surface of nickel is smooth and fine grained. and with antimony and lead to form babbitt. and will boil under the torch. In a spark test. It serves as the best container for preserving perishable focal. Tin gives off no sparks in a spark test. and is corrosion resistant. 29. Tin can be die cast. medium-strength metal having very good corrosion resistance. Tin is not weldable. Titanium is a very soft. somewhat ductile. The fracture surface of tin is silvery white and fairly smooth. specific gravity of 7. A second major use of tin is as an alloying element. 1.00 percent nickel. and its
. (11) Titanium (Ti).950 kPa) and Brinell hardness number of 30. (a) General.(g) Fracture. Babbitt alloy tin has tensile strength of 10. Pure tin has tensile strength of 2800 psi (19. melting point of 450°F (232°C). in the form of foil.40 percent iron. (10) Tin (Sn). It has a very high resistance to corrosion and can be welded.00 percent copper. is often used in wrapping food products. and soldered. cold worked (extruded). 0. (h) Spark test.29. and 0. Tin is alloyed with copper to produce tin brass and bronze.15 percent carbon. Tin is a very soft. Tin melts at 450°F (232°C). (f) Appearance. malleable. After use. (g) Fracture test. with lead to produce solder.10 percent silicon. The major application of tin is in coating steel. corrosion resistant metal having low tensile strength and high crystalline structure. (e) Properties. Tin is silvery white in color.00 to 80. silvery white. (i) Monel metal. nickel produces a very small amount of short.306 kPa). (h) Spark test. or after contact with chemical solutions. it resembles untarnished nickel. (c) Capabilities. Tin. It has a high strength to weight ratio. (d) Limitations. It is used in coating metals to prevent corrosion.000 psi (68. and some of the luster is lost. machined. the silver-white color takes on a yellow tinge. (b) Uses. 1.00 percent manganese. In appearance. (a) General.

making powder for fireworks. and as an alloying agent in production of high-speed steel. Tungsten is used in making light bulb filaments.000 psi. and of medium length. Titanium has low impact and creep strengths. heavy. die and tool steels. frame assemblies. Brinell hardness number of 200. armorplate. and fusion welded using inert gas. ammunition tracks. The inert gas welding process is recommended to reduce contamination of the weld metal. (e) Properties. phonograph needles. Alloy titanium has a Brinell hardness number of 340. (a) General. melting point of 3300°F (1851°C). specific gravity of 4. It is also used as an alloying agent in nonconsumable welding electrodes. (b) Uses. shiny. armor plate. spot-and seam-welded. Titanium is a soft. and hard metal carbide cutting tools. which is used widely in welding electrode coatings. (d) Limitations. Titanium can be machined at low speeds and fast feeds.5. Tungsten is a hard. engine nacelles. The solution will not react with titanium.tensile strength increases as the temperature decreases. brilliant white. aircraft firewalls. (g) Spark test. and in the manufacture of turbine blades. Its most important compound is titanium dioxide. copper. and can be distinguished from steel by a copper sulfate solution. formal. Oxidation causes this metal to become quite brittle.000 psi. Titanium has low impact strength. It is used as a stabilizer in stainless steel so that carbon will not be separated during the welding operation. and low creep strength at high temperatures (above 800°F (427°C)). steel. (f) Appearance test. as well as seizing tendencies. It can only be cast into simple shapes. and nickel. It is also used as an additive in alloying aluminum. at temperatures above 800°F (427°C). and projectiles. Pure titanium has a tensile strength of 100. nonmagnetic metal which will melt at approximately 6150°F (3400°C). (c) Capabilities. tensile strength of 150. (12) Tungsten (W). The free element is separated by heating the oxide with aluminum or by the electrolysis of the solution in calcium chloride. Titanium is a metal of the tin group which occurs naturally as titanium oxide or in other oxide forms. The sparks given off are large. Titanium alloys look like steel. and good corrosion resistance. silvery-white metal burns in air and is the only element that burns in nitrogen. magnesium. and a high strength/weight ratio (twice that of aluminum alloy at 400°F (204°C)).
. (b) Uses. and mortar base plates. but will leave a coating of copper on steel. and it cannot be welded by any gas welding process because of its high attraction for oxygen.

building equipment. cold worked (extruded).
. and flux. (13) Zinc (Zn). 2. Zinc can be soldered or welded if it is properly cleaned and the heat input closely controlled.397. Tungsten has a melting point of 6170 ± 35°F (3410 ± 19°C). ornaments.000 psi (82. has tensile strength of 105. Examples of items made in this way are galvanized pipe. (b) Uses.(c) Capabilities. a Brinell hardness number of 38. instrument panels. (f) Appearance. widely used in paint and rubber. and zinc dust. is ductile. orange streaks in a spark test. Tungsten can be cold and hot drawn. and bolts. toys. nails. tubing. and is brittle at 220°F (104°C).000 psi (186. thermal conductivity of 0. Ito is easy to machine. which is used in the manufacture of explosives and chemical agents. Those alloys that are made up primarily of zinc itself. and is produced by powered metallurgy (sintering process).000 psi (723. (c) Capabilities. Zinc is a medium low strength metal having a very low melting point. (d) Limitations. (a) General. munitions. Zinc can be cast. and welded. straight. Do not use zinc die castings in continuous contact with steam. (g) Spark test. a melting point of 790°F (421°C). Other forms of zinc include zinc oxide and zinc sulfide. Tungsten is hard to machine. cooking utensils. Galvanizing metal is the largest use of zinc and is done by dipping the part in molten zinc or by electroplating it. Zinc is also used as an alloying element in producing alloys such as brass and bronze. Typical parts made with zinc alloy are die castings. a specific gravity of 19.740 kPa) (cast) and 27. Tungsten is steel gray in color. Tungsten produces a very small volume of short. sheet metal. (e) Properties.32. wet and dry batteries.1. machined. a specific gravity of 7. requires high temperatures for melting. and is a dull white color. pipe organ pipes. Zinc has a tensile strength of 12. fuse plugs. is corrosion resistant. carburetor and fuel pump bodies. wire.165 kPa) (rolled).975 kPa). but coarse grain zinc should be heated to approximately 180°F (82°C) to avoid cleavage of crystals. (d) Limitations. (e) Properties. 1.

Sometimes. No sparks given off in a spark test. and the metal boils under the torch. The metal boils when heated with the oxyacetylene flame. Except for those made of lead and tin. 2.
Section II.(f) Appearance. Die castings are usually alloys of zinc. Zinc die castings can be recognized by their low melting temperatures. (g) Fracture test. can be welded with a carburizing flame using tin or aluminum solders as filler metal. after thorough cleaning. generally silvery white in color (like aluminum). Both zinc and zinc alloys are blue-white in color when polished. (h) Spark test. or tin. Melting points are low. and is almost as smooth as a machined surface. Fracture test. (i) Zinc die castings. STANDARD METAL DESIGNATIONS
7-4. (e) Torch test. These are usually made with alloys of aluminum. but the die casting is lighter in weight and softer. 1. Appearance test. the diecast part can be used as a pattern to make a new brass casting. Fractured surface is white and somewhat granular. lead. GENERAL
. (c) Fracture test. If necessary. (14) White metal die castings. Spark test. (b) Appearance. Torch test. Zinc and zinc alloys give off no sparks in a spark test. A die casting. and sometimes of intricate design. lead. 3. magnesium. magnesium. aluminum. They are light in weight. Zinc die castings give off no sparks. die castings darkened by use may be mistaken for malleable iron when judged simply by looks. The surface of a zinc die casting is white and has a slight granular structure. and tin. 4. (a) General. and oxidize to gray. The surface is much smoother than that produced by castings made in sand. they are generally light in weight and white in color. Zinc fractures appear somewhat granular. A die-cast surface is much smoother than that of a casting made in sand. (d) Spark test.

b.The numerical index system for the classification of metals and their alloys has been generally adopted by industry for use on drawings and specifications. and the average carbon content percentage are given. and in some cases five digits are used to designate certain alloy steels. Numbers are used to designate different chemical compositions. the class to which the metal belongs. This system has been expanded. In this system. Two letters are often used as a prefix to the numerals.
. 7-5. The letter H is sometimes used as a suffix to denote steels manufactured to meet hardenability limits. The letter C indicates basic open hearth carbon steels. STANDARD DESIGNATION SYSTEM FOR STEEL a. the predominant alloying agent. and E indicates electric furnace carbon and alloy steels. A four-digit number series designates carbon and alloying steels according to the types and classes shown in table 7-8.

e.E. The S. and chrome-molybdenum.E.--S. the system deviates from this rule. COMPARISION A. nickelchromium.21 indicates a range of 0. E.40 percent carbon. In a few cases. A. Steel Specifications The ever-growing variety of chemical compositions and quality requirements of steel specifications have resulted in several thousand different combinations of chemical elements being specified to meet individual demands of purchasers of steel products.A. and some carbon ranges relate to the ranges of manganese. The complete designation system is shown in table 7-9. The American Iron and Steel Institute has now gone further in this regard with a
. The number 4340 indicates a nickel-chrome-molybdenum metal with 0.18 to 0. phosphorous. S.23 percent carbon. Steel Specifications The following numerical system for identifying carbon and alloy steels of various specifications has been adopted by the Society of Automotive Engineers. developed a system of nomenclature for identification of various chemical compositions which symbolize certain standards as to machining. such as manganese.I. The first two digits indicate the major alloying metals in a steel. chromium. For example.A. and carburizing performance. and other elements. The number 2340 by this system indicates a nickel steel with approximately 3 percent nickel and 0. sulfur. The last digits indicate the approximate middle of the carbon content range in percent.c. heat treating.S.40 percent carbon.I. The system designates the major elements of a steel and the approximate carbon range of the steel.
f. 0. d. It also indicates the manufacturing process used to produce the steel.

the 3 indicates a manganese aluminum alloy. The letters identify which alloying elements were used in the magnesium alloy (table 7-11). the letter A means 1. the aluminum content is 99.b. the 1 indicates a minimum aluminum composition of 99 percent. and C means 3. f. The first digit represents the major alloying element. and the 17 indicates a commonly used commercial alloy. designate the percentage of the elements in the magnesium alloy. except in the 1XXX class. the 2 indicates the second modification of this particular alloy. STANDARD DESIGNATION SYSTEM FOR MAGNESIUM AND MAGNESIUM ALLOYS a. d. The last two digits seine only to identify different aluminum alloys which are in common commercial use. The second digit identifies alloy modifications (a zero means the original alloy).
7-7. In number 1017. For example.17 percent. in hundredths of one percent. Wrought magnesium and magnesium alloys are identified by a combination of letters and numbers. There may be an additional letter following the percentage designators which indicates the alloy modifications. In the 1XXX class. the last two digits indicate the aluminum content above 99 percent. B means 2. the 0 indicates it is the original composition. c. e. In number 3217. In this example. Numbers. The various classes of aluminum and aluminum alloys are identified by numbers as shown in table 7-10. which may follow the letters. and the 17 indicates the hundredths of one percent of aluminum above the 99 percent minimum composition. g.
.

In the identification number AZ93C. The second digit gives the percentage of the second letter (table 7-12). The first digit. always indicates the percentage of the first letter. 9 in this example. the Z indicates zinc.b. the 3 indicates there is 3 percent zinc in the alloy. the A indicates aluminum. A in this example. and the C indicates the third modification to the alloy. the 9 indicates there is 9 percent aluminum in the alloy.
.

. however. another space. has established an alloy designation system that is widely accepted in North America. and the data presented will provide starting point guidelines. This system has been updated so that it now fits the unified numbering system (UNS). and. It provides one unified numbering ring system which includes all of the commercially available metals and alloys. It is not a specification system but rather a method of identifying and grouping different coppers and copper alloys. The welding information is the same whether the material is cast or rolled. There are over 300 different wrought copper and copper alloys commercially available. The information shown by table 7-13 is a grouping of these copper alloys by common names which normally include the constituent alloys. Temper designations may be added to the basic magnesium designation. The Copper Development Association. two zeros. There may be those alloys within a grouping that may have a composition sufficiently different to create welding problems. There are two categories.c. 7-8. finally. three digits. wrought materials and cast materials. The UNS designation consists of the prefix letter C followed by a space. STANDARD DESIGNATION SYSTEM FOR COPPER AND COPPER ALLOYS a. the two being separated by a dash. Inc. Welding information for those alloy groupings is provided. These are the exception. The temper designations are the same as those used for aluminum (see Heat Treatment of Steel in Chapter 12). b..

.

followed by the percentage number(s) and the chemical symbols(s) of the alloying element(s).
. Ti. However.5 Sn would indicate that 5 percent aluminum and 2-1/2 percent tin alloying elements are present in the titanium metal. Ti-5 A1-2.7-9. these compositions are generally designated by using the chemical symbol for titanium. For example. STANDARD DESIGNATION SYSTEM FOR TITANIUM There is no recognized standard designation system for titanium and titanium alloys.

Rolled steel has fine surface lines running in one direction. and therefore do not require preheating or postheating except in special cases. 7-7). phosphorous 0. forked sparklers. dark gray surface except where machined. Cast steel has a rough. and sulfur 0. and worked when either hot or cold.25 percent. General.50 percent.10 to 0. no difficulties are encountered when welding low carbon steels. The low carbon (mild) steels include those with a carbon content of up to 0. Forged steel is usually recognizable by its shape. manganese from 0. and resistance welding processes.Section III. hammer marks.30 percent (fig.
b. carbon ranges from 0.50 percent maximum. Copper coated low carbon rods should be used for welding low carbon steel. LOW CARBON STEELS a. Steels in this range are most widely used for industrial fabrication and construction. ductile. Properly made low carbon steel welds will equal or exceed the base metal in strength. yellow-orange streaks that have a tendency to burst into white. Steel gives off sparks when melted and solidifies almost instantly. They can be machined and are readily welded. and the spark test yields sparks with long. Low carbon steels can be easily welded with any of the arc. such as when heavy sections are to be welded. These low carbon steels do not harden appreciably when welded. The fracture color is bright crystalline gray. sheared. or fins. gas. In most low carbon steels. punched. The rod sizes for various plate thicknesses are as follows: Plate thickness Rod diameter
. GENERAL DESCRIPTION AND WELDABILITY OF FERROUS METALS
7-10. In general.25 to 0.40 percent maximum. can be rolled. Low carbon steels are soft.

7 mm) 1/2 in.4 mm) rods by properly controlling the puddle and melting rate of the rod. Either the forehand or backhand welding method may be used (para 6-23 through 6-24). (6.2 mm) 3/16 in. (1.5 to 12. (3.2 mm) 1/8 to 3/8 in. c.2 to 9.8 mm) 1/4 in. (12. and the weld badly scarred. (3.5 mm) are available for heavy welding. The resultant grain structure of the weld metal will be large. the strength lowered.7mm) and heavier
1/16 in.6 mm) 1/8 in. The flame should be adjusted to neutral. g. (7. depending on the thickness of the plates being welded. The low carbon steels do not harden in the fusion zone as a result of welding. e. heavy welds can be made with the 3/16 or 1/4 in.
.
d. However.1/16 to 1/8 in. (4. (1.9 to 9. The type of preparation (fig.6 to 3. Metal-Arc Welding. 7-8) is determined by the plate thickness and the welding position. because this will cause the metal to boil and spark excessively. (4. f.5 mm) 3/8 to 1/2 in. The joints may be prepared by flame cutting or machining. The molten metal should not be overheated. (9.4 mm) NOTE
Rods from 5/16 to 3/8 in.8 or 6.

MEDIUM CARBON STEELS
.0 or 4. the best results are obtained by using string beads throughout the weld. This will reduce the amount of distortion in the welded structure. or skip. (2) Low carbon sheet or plate materials that have been exposed to low temperatures should be preheated slightly to room temperature before welding. This will prevent warpage or distortion. 7-11.2 mm) in thickness. The first bead should be thoroughly cleaned by chipping and wire brushing before additional layers of weld metal are deposited. oxides. The motion of the electrode should be controlled so as to make the bead uniform in thickness and to prevent undercutting and overlap at the edges of the weld. and will minimize residual stresses. (6) When welding heavy sections that have been beveled from both sides. because the deposited metal tends to pull the plates together. the plain square butt joint type of edge preparation may be used. (3. When overhead welding. This shrinkage is less severe in arc welding than in gas welding. or vertical positions. Additional passes of the filler metal should be made with a 5/32 or 3/16 in. (4) The backstep. The parts should be tack welded in place at short intervals along the seam. Carbon-Arc Welding. A gaseous shield should be provided around the molten base.14 percent). (3. and cause brittleness in the welded joint. which are prepared in a manner similar to that required for metal-arc welding. (5) Heavy plates should be beveled to provide an included angle of up to 60 degrees. horizontal. (3) In welding sheet metal up to 1/8 in. Filler metal.0 mm) electrode is suitable for this purpose. or root. and slag before additional metal is deposited. (4. All slag and oxides must be removed from the surface of the completed weld to prevent rusting. depending on the thickness. the edges should be spaced to allow for shrinkage. The first. the weave beads should be deposited alternately on one side and then the other. h. Failure to observe these precautions can cause the weld metal to absorb an excessive amount of carbon from the electrode and oxygen and nitrogen from the air.8 mm) electrode. A flux should be used on the joint and filler metal should be added as in oxyacetylene welding.(1) When metal-arc welding low carbon steels. Low carbon sheet and plate up to 3/4 in. and spacing of approximately 1/8 in. The passes should be made with a weaving motion for flat. the bare.0 mm) in thickness can be welded using the carbon-arc welding process.2 mm) will be sufficient. should also be provided. thin coated or heavy coated shielded arc types of electrodes may be used. These electrodes are of low carbon type (0. (19. When long seams are to be welded in these materials. bead should be made with an electrode small enough in diameter to obtain good penetration and fusion at the base of the joint. Each bead should be cleaned thoroughly to remove all scale. A 1/8 or 5/32 in. by means of a flux coated welding rod. Welding must be done without overheating the molten metal. (3.2 or 4. welding technique should be used for short seams that are fixed in place.10 to 0. The arc is struck against the plate edges.

By using this procedure. particularly in thicker sections. the entire piece should be heat treated to restore its original properties.30 to 0.
. c. The entire welded part should be stress relieved by heating to between 1100 and 1250°F (593 and 677°C) for one hour per inch (25. the weld zone will become hardened if cooled rapidly. e. and resistance welding processes. and must be stress relieved after welding. similar to those used for metal-arc welding of low carbon steels. During welding. The preheating temperature may be checked by applying a stick of 50-50 solder (melting point 450°F (232°C)) to the plate at the joint. d. the weld metal is caused to wash up against the side of the joint and fuse with it without deep or excessive penetration.55 percent carbon. f. However. When welding with low carbon steel electrodes. Welding with a carburizing flame causes the metal to heat quickly. These steels may be heat treated after fabrication and used for general machining and forging of parts which require surface hardness and strength. these steels are better welded by the metal-arc process with mild steel shielded arc electrodes. g.45 percent) and the thickness of the steel. and then slowly cooling. When heat treated steels are welded. Care should be taken to slowly cool the parts after welding to prevent cracking of the weld. the welding heat should be carefully controlled to avoid overheating the weld metal and excessive penetration into the side walls of the joint. and noting when the solder begins to melt. keep the following general techniques in mind: (1) The plates should be prepared for welding in a manner similar to that used for welding low carbon steels. They are manufactured in bar form and in the cold rolled or the normalized and annealed condition. the low-hydrogen type electrodes should be used. and a brazing flux. Electrodes of the low-carbon. This permits welding at higher speeds. Small parts should be annealed to induce softness before welding. because heat is given off when steel absorbs carbon. gas. a good bronze rod. depending on the carbon content (0. After welding. and the puddle of metal kept as small as possible to make a sound joint. b. are satisfactory for welding medium carbon steels.25 to 0.a. The parts should be preheated at the joint and welded with a filler rod that produces heat treatable welds. Cooling can be accomplished by covering the parts with fire resistant material or sand. This control is accomplished by directing the electrode more toward the previously deposited filler metal adjacent to the side walls than toward the side walls directly. With higher carbon and manganese content. they should be preheated from 300 to 500°F (149 to 260°C).4 mm) of thickness. Medium carbon steels are non-alloy steels which contain from 0. Medium carbon steels may be welded with any of the arc. straight or reverse polarity type. General. Medium carbon steels can be brazed by using a preheat of 200 to 400°F (93 to 204°C). When welding mild steels. heavy coated. Either a low carbon or high strength rod can be used for welding medium carbon steels. The welding flame should be adjusted to slightly carburizing.

and steel castings cannot be hardened. d. sheet. heat treatment is necessary. Each bead or layer of weld metal will refine the grain in the weld immediately beneath it. Low carbon steel. The preheating temperature can be checked with a pine stick. Since high carbon steels melt at lower temperatures than low and medium carbon steels. High carbon steel can be hardened by heating to a good red and quenching in water. The welding heat changes the properties of high carbon steel in the vicinity of the weld. 7-12. Because of the high carbon content and the heat treatment usually given to these steels. The unfinished surface of high carbon steels is dark gray and similar to other steels. and the melting surface has a cellular appearance. High carbon steels should be preheated from 500 to 800°F (260 to 427°C) before welding. These steels are used to manufacture tools which are heat treated after fabrication to develop the hard structure necessary to withstand high shear stress and wear. The high carbon steels are difficult to weld because of the hardening effect of heat at the welded joint. HIGH CARBON STEELS a. b. (3) When possible. Overheating is indicated by excessive sparking of the molten metal. Molten high carbon steel is brighter than low carbon steel. Tool steel is harder and more brittle than plate steel or other low carbon material. They are manufactured in bar. The area of these hard zones in the base metal can be kept to a minimum by making the weld with a series of small string or weave beads. This type of flame tends to produce sound welds. The flame should be adjusted to carburizing. care should be taken not to overheat the weld or base metal. and wire forms. It sparks more freely than low carbon (mild) steel.55 percent. High carbon steels usually produce a very fine grained fracture. wrought iron. (4) In welding medium carbon steels with stainless steel electrodes. brushed. Stress relieving is normally used when joining mild steel. To restore the original properties. General. Welding should be completed as soon as possible and the amount of sparking should be used as a check on the welding heat. and will anneal and lessen the hardness produced in the base metal by the previous bead. When depositing weld metal in the upper layers of welds made on heavy sections.
. and cleaned prior to the laying of another bead. which will limit the heat input. c. and the sparks are whiter. (5) Each successive bead of weld should be chipped. their basic properties are impaired by arc welding. the metal should be deposited in string beads in order to prevent cracking of the weld metal in the fusion zone.(2) High welding heats will cause large areas of the base metal in the fusion zone adjacent to the welds to become hard and brittle. and high carbon alloys should be annealed. the finished joint should be heat treated after welding. High carbon steels include those with a carbon content exceeding 0. the weaving motion of the electrode should not exceed three electrode diameters. and in the annealed or normalized and annealed condition in order to be suitable for machining before heat treatment. whiter than low carbon steels. which will char at these temperatures.

4 mm) of thickness. (2) The same procedure for edge preparation. because the strength of the joint is not as high as the original base metal. molybdenum. In some cases. and then slowly cooling. and heat treated after welding to restore its original properties. b. Carbon is provided in tool steel to help harden the steel for cutting and wear resistance.e. Iron is the predominant element in the composition of tool steels. Use the surface fusion procedure prescribed for medium carbon steels (para 7-11). cleaning of the welds. nickel. and sequence of welding beads as prescribed for low and medium carbon steels also applies to high carbon steels. because this can cause carbon to be picked up from the base metal. and dies are perhaps the hardest. so the properties of the base metal are not seriously affected. elements are added to retain the size and shape of the tool during its heat treat hardening operation. Metal-arc welding in high carbon steels requires critical control of the weld heat. a high carbon welding rod should be used to make the joint. high carbon steel parts are sometimes repaired by building up worn surfaces. which in turn will make the weld metal hard and brittle. or to make the hardening operation safer and to provide red hardness so that the tool retains its hardness and strength when it becomes extremely hot. Steels used for making tools. the entire piece should be stress relieved by heating to between 1200 and 1450°F (649 and 788°C) for one hour per inch (25. h. Other elements are added to provide greater toughness or strength. TOOL STEELS a. cobalt. 7-13. Either mild or stainless steel electrodes can be used with high carbon steels. Brazing should only be used in special cases. In general. strongest. Control of the welding heat can be accomplished by depositing the weld metal in small string beads. manganese. A spark test shows a moderately large volume of white sparks having many fine. Excessive puddling of the metal should be avoided. g. When this is done. This process does not require temperatures as high as those used for welding. If the parts can easily be softened before welding. minor repairs to these steels can be made by brazing. and toughest steels used in industry. tool steels are medium to high carbon steels with specific elements included in different amounts to provide special characteristics. repeating bursts. General.
. f. punches. The following techniques should be kept in mind: (1) The welding heat should be adjusted to provide good fusion at the side walls and root of the joint without excessive penetration. The entire piece should then be heat treated to restore the original properties of the base metal. Fusion between the filler metal and the side walls should be confined to a narrow zone. Either a medium or high carbon welding rod should be used to make the weld. After welding. the piece should be annealed or softened by heating to a red heat and cooling slowly. (3) Small. In some cases. The piece should then be welded or built up with medium carbon or high strength electrodes. Other elements added include chromium.

Steels in the tool steels group have a carbon content ranging from 0. and staking dies. A less severe quench is the oil quench. d. If arc welding must be done. blanking dies. and vanadium.
. forming dies. Certain tool steels are made for producing die blocks. the steel should be heat treated to restore its original properties. others for hot working. extrusion dies. (1) Class I steels are used to make tools that work by a shearing or cutting actions. either mild steel or stainless steel electrodes can be used. plastic molds. (4) Class IV steels are used to make dies that work under heavy pressure and that produce a flow of metal or other material caressing it into the desired form. forging dies. shearing dies. The least drastic quench is cooling in air (air-hardening steels). heading dies. taking care not to overheat the molten metal. The welding should be done as quickly as possible. Another way to classify tool steels is according to the type of quench required to harden the steel.55 percent.tungsten. Drill rods can be used as filler rods because their high carbon content compares closely with that of tool steels. This is based on class numbers. The tool or die steels are designed for special purposes that are dependent upon composition. f. This includes bending dies. and trimming dies. Uniformly high preheating temperatures (up to 1000°F (583°C)) must be used when welding tool steels. such as cutoff dies. embossing dies. The most severe quench after heating is the water quench (water-hardening steels). c. and die cast molding dies. Tool steels and dies can also be classified according to the work that is to be done by the tool. This includes crimping dies. some are made for producing molds. (3) Class III steels are used to make tools that act upon the material being worked by partially or wholly reforming it without changing the actual dimensions. This includes drawing dies. and twisting dies. e. They are rarely welded by arc welding because of the excessive hardness produced in the fusion zone of the base metal. g. reducing dies. The welding flare should be adjusted to carburizing to prevent the burning out of carbon in the weld metal. either hot or cold.83 to 1. After welding. obtained by cooling the tool steel in oil baths (oil-hardening steels). (2) Class II steels are used to make tools that produce the desired shape of the part by causing the material being worked. to flow under tension. h. folding dies. the same precautions should be taken as those required for welding high carbon steels (para 6-12). and others for high-speed cutting application. In general.

and a given strength is secured with less material weight. b. rather than a water quench. Most of these steels depend on a special heat treatment process in order to develop the desired characteristic in the finished state. and gives high strength with little loss in ductility. and other special properties. the edge of the plate should be preheated to prevent the formation of hard zones in the base metal. air-hardening dies. Chromium in large amounts shortens the spark stream to one half that of the same steel without chromium. k. and hot work tools.i. The edges should then be preheated up to 1000°F (538°C). The carbon picked up from the base metal by the filler metal will cause the weld to become glass hard. There are four types of die steels that are weld repairable. Nickel increases the toughness. When welding tool steels. The weld metal should be deposited in small string beads to keep the heat input to a minimum. General. A large number and variety of obtain high strength. (2) Nickel alloy steels. is used for hardening. corrosion alloy steels have been developed to resistance. (2) High carbon electrodes should not be used for welding tool steels. whereas the mild steel weld metal can absorb additional carbon without becoming excessively hard. Alloy steels have greater strength and durability than other carbon steels. and ductility of steels. corrosion resistance. HIGH HARDNESS ALLOY STEELS a. High-speed tools can also be repaired. the following techniques should be kept in mind: (1) If the parts to be welded are small. A flux suitable for welding cast iron should be used in small quantities to protect the puddle of high carbon steel and to remove oxides in the weld metal. High hardness alloy steels include the following: (1) Chromium alloy steels. they should be annealed or softened before welding. The nickel spark has a short. and shock resistance. depending on the carbon content and thickness of the plate. Chromium is used as an alloying element in carbon steels to increase hardenability. and lowers the hardening temperature so that an oil quench. sharply defined dash of brilliant light just before the fork. Welding Technique. oilhardening dies. strength. 7-14. The welded part should then be heat treated to restore its original properties. j. (3) When welding with stainless steel electrodes. Welding should be done with either a mild steel or high strength electrode. These are water-hardening dies.
. but does not affect the stream’s brightness. the application procedure is the same as that required for medium and high carbon steels. high hardness. In general.

(3) High chromium-nickel alloy (stainless) steels. In a spark test. Steels containing manganese produce a spark similar to a carbon spark. the impact fatigue proper is impaired. and are due to the formation of a very thin oxide film which forms on the surface of the metal. Molybdenum is sometimes combined with chromium. (4) Manganese alloy steels. curved. Wear resistance is improved with molybdenum content above about 0. corrosion. Sparks are straw colored near the grinding wheel. and forging. These elements are used as additional alloying agents in low carbon content. Tungsten. which is the depth of hardening possible through heat treatment. Alloy steels containing vanadium
. Their stainless. When used in larger quantities. Vanadium is used to help control grain size. tungsten produces a steel that retains its hardness at high temperatures. corrosion resistant steels. Carrier lines may be from dull red to orange. and in combination with other alloys. dense grain when used in relatively small quantities.75 percent. which can be seen even in fairly strong carbon bursts. (5) Molybdenum alloy steels. It is added to steel during manufacture to remove oxygen. Molybdenum alloy steels contain either nickel and/or chromium. tends to produce a fine. These high alloy steels cover a wide range of compositions. tungsten will show a dull red color in the spark stream near the wheel. A moderate increase in manganese increases the volume of the spark stream and the intensity of the bursts. yet resists tempering. as an alloying element in tool steel. depending on the other elements present.60 percent molybdenum. providing the tungsten content is not too high. Manganese is used in steel to produce greater toughness. It also shortens the spark stream and decreases the size of or completely eliminates the carbon burst. A steel containing more than a normal amount of manganese will produce a spark similar to a high carbon steel with a lower manganese content.60 percent molybdenum. This element is usually used in combination with chromium or other alloying agents. orange spear points at the end of the carrier lines. Still lower tungsten content causes small. They support resistance to intergranular corrosion after the metal is subjected to high temperatures for a prolonged period of time. There is a medium volume of streaks which have a moderate number of forked bursts. (6) Titanium and columbium (niobium) alloy steels. The impact fatigue property of the steel is improved with up to 0. wear resistance. Above 0. (8) Vanadium alloy steels. and white near the end of the streak. tungsten. Steels containing this element produce a characteristic spark with a detached arrowhead similar to that of wrought iron. white bursts to appear at the end of the spear petit. from 17 to 20 percent. easier hot rolling. An increase in manganese content decreases the weldability of steel. and heat resistant properties vary with the alloy content. A tungsten steel containing about 10 percent tungsten causes short. It tends to increase hardenability and causes marked secondary hardness. (7) Tungsten alloy steels. Molybdenum increases hardenability. or vanadium to obtain desired properties.

These steels are usually special alloy compositions designed for cutting tools. Stainless steel electrodes are effective where preheating is not feasible or desirable.500 kPa) and a tensile strength of 100. and the welding heat should be controlled by depositing the metal in narrow string beads. therefore. High yield strength.300 kPa). Structural members fabricated from these high strength steels may have smaller cross-sectional areas than common structural steels and still have equal strength. (9) Silicon alloy steels. Reliable welding of high yield strength. low alloy structural steels (constructional alloy steels) are special steels that are tempered to obtain extreme toughness and durability. released into the arc. The carbon content ranges from 0.550 to 689.000 to 100. use only low hydrogen (MIL-E-18038 or MIL-E-22200/1) electrodes to prevent underbead cracking. depending upon size and shape. in order to minimize the formation of hard zones. A spark test will show a few long. in the base metal adjacent to the weld. low alloy structural steels can be performed by using the following guidelines: CAUTION To prevent underbead cracking. The special alloys and general makeup of these steels require special treatment to obtain satisfactory weldments. only low hydrogen electrodes should be used when welding high yield strength. The molten metal should not be overheated. Welding Technique. c. These steels are also more corrosion and abrasion resistant than other steels. tough steel. 7-15. these alloys produce a spark very similar to low carbon steels. (10) High speed tool steels. In many cases. LOW ALLOY STRUCTURAL STEELS a.80 percent. low-carbon steels containing specific.000 psi (689. forked spades which are red near the wheel. or layers. These steels are special. whose composition is similar to that of the base metal.
.000 to 140. the procedures for welding medium carbon steels (para 7-11) and high carbon steels (para 7-12) can be used in the welding of alloy steels. and absorbed by the molten metal. small amounts of alloying elements.500 to 965. low alloy structural steels. Many of these steels can be welded with a heavy coated electrode of the shielded arc type. Low carbon electrodes can also be used with some steels.000 psi (620. Silicon is added to steel to obtain greater hardenability and corrosion resistance. General. They are quenched and tempered to obtain a yield strength of 90. HIGH YIELD STRENGTH.70 to 0. (1) Correct electrodes.produce sparks with detached arrowheads at the end of the carrier line similar to those produced by molybdenum steels. b. except by the furnace induction method. and straw colored near the end of the spark stream. Hydrogen is the number one enemy of sound welds in alloy steels. if possible. Underbead cracking is caused by hydrogen picked up in the electrode coating. They are difficult to weld. It is often used with manganese to obtain a strong. Heat treated steels should be preheated. In a spark test.

or 18. immediately upon opening the container.05 percent vanadium may brittle if stress relieved. (4. Electrodes are identified by classification numbers which are always marked on the electrode containers.2 mm) in diameter are the most commonly used. In the event that the electrodes are not in an airtight container. Table 7-14 lists electrodes used to weld high yield strength. the last two nunbers of the classification should be 15. Wire electrodes for submerged arc and gasshielded arc welding are not classified according to strength. Low Hydrogen Electrode Selection. low alloy structural steels. Baked electrodes should. put them in a ventilated baking oven and bake for 1-1/4 hours at 800°F (427°C).
d. Welding wire and wire-flux combinations used for steels to be stress relieved should contain no more than 0. When using either the submerged arc or gas metal-arc welding processes to weld high yield
. If the electrodes are in an airtight container. c. Table 7-15 is a list of electrodes currently established in the Army supply system. Testing for moisture should be in accordance with MIL-E-22200. while still warm. 16.(2) Moisture control of electrodes. Selecting Wire-Flux and Wire-Gas Combinations. place them. Weld metal with more than 0. in a ventilated holding oven set at 250 to 300°F (121 to 149°C). NOTE Moisture stabilizer NSN 3439-00-400-0090 is an ideal holding oven for field use (MIL-M45558). For low hydrogen coatings. be placed in the holding oven until used.0 and 3. Electrodes of 5/32 and 1/8 in. Electrodes must be kept dry to eliminate absorption of hydrogen. since they are more adaptable to all types of welding of this type steel.05 recent vanadium.

Table 7-16 contains suggested preheating temperatures. at 20 volts and 300 amps. (2) Heat input nomograph. the line intersects column 2 at the value 6. Read the heat units at the point where this second line intersects column 4. or 30. It is important to avoid excessive heat concentration in order to allow the weld area to cool quickly. e. find the volts value in column 1 and draw a line to the amps value in column 3. (1) General.strength./min.
. At 12 in. Either the heat input nomograph or the heat input calculator can be used to determine the heat input into the weld. draw another line to the in. Preheating. low alloy structural steels to lower strength steels the wire-flux and wire-gas combination should be the same as that recommended for the lower strength steels. (25. For welding plates under 1. From the point where this line intersects colunm 2./min value in column 5.000 joules/in. above 50°F (10°C) is not required except to remove surface moisture metal. For example. the heat input is determined as 30 heat units. Welding Heat.4 mm) thick. To use the heat input nomograph (fig. The heat units represent thousands of joules per inch. 7-9).0 in.
f.

As with the nomograph. or preheat temperature until the calculated heat input is within the proper range. To determine welding heat input using the calculator. They are not applicable to multiple-arc or electroslag welding. If no suitable material is available. rotate until the value on the volts scale is aligned directly opposite the value on the speed (in. travel speed./min) scale. light cardboard. adjust the amperes.(3) Heat input calculator. After the two pieces are cut out.) For welding conditions exceeding
. heat units represent thousands of joules per inch. or some similar device. flux-cored arc. or other high heat input vertical-welding processes. If the calculated value is too high. Check the heat input value obtained from the nomograph or calculator against the suggested maximums in tables 7-17 and 7-18. The value on the amps scale will then be aligned directly opposite the calculated value for heat units. a hole is punched in the center of each. The heat input calculator can be made by copying the pattern printed on the inside of the back cover of this manual onto plastic. since welds made by these in the "T-1" steels should be heat treated by quenching and tempering. shielded metal-arc. or other suitable material and cutting out the pieces. gas tungsten-arc. submerged arc. the calculator may be assembled by cutting the pattern out of the back cover. which will allow the pieces to rotate. and gas metalarc processes. They are then assembled using a paper fastener. (4) Maximum heat input. (The tables are applicable only to singlearc.

Fillet welds should be smooth and correctly contoured. Avoid toe cracks and undercutting. if needed. it must be restricted to a partial weave pattern. Never use a full weave pattern. The partial weave pattern should not exceed twice the diameter of the electrode. especially if the
. Best results are obtained by a slight circular motion of the electrode with the weave area never exceeding two elect-rode diameters.the range of the nomograph or calculator. Reliable welding of high yield strength. Avoid using the weave pattern. Peening of the weld is sometimes recommended to relieve stresses while cooling larger pieces. low alloy structural steel can be per formal by choosing an electrode with low hydrogen content or selecting the proper wire-flux or wire gas combination when using the submerged arc or gas metal arc processes. Welding Process. Use a straight stringer bead whenever possible. the heat input can be calculated using the following formula:
g. Skip weld as practical. Air-hammer peening of fillet welds can help to prevent cracks. Electrodes used for fillet welds should be of lower strength than those used for butt welding. however.

A bead is laid in the toe area. and silicon. This provides a cast iron with higher hardness. b. then ground off prior to the actual fillet welding. 7-16. This can be
.5 percent. but is usually such that it is primarily perlite with many graphite flakes dispersed throughout. General. and water preps. heads. It can. Austenitic cast irons have a high degree of corrosion resistance. CAST IRON a. This structure provides a greater degree of ductility or malleability of the casting. rather than the normal flake shape in gray cast iron. however. Gray iron has a variety of compositions. be welded with the metal-arc process without preheating if the welding heat is carefully controlled. and for automobile engine blocks. brackets. Because of the additional material involved in fillet welding. and covers. (1) The most widely used type of cast iron is known as gray iron. which increases its ductility. A soft steel wire pedestal can help to absorb shrinkage forces.welds are to be stress relieved. almost all the carbon is in the combined form. Because of this characteristic. Cast iron is rarely used in structural work except for compression members. manifolds. which is modified by additions of nickel and other elements to reduce the transformation temperature so that the structure is austenitic at room or normal temperatures. molybdenum. A cast iron is an alloy of iron. preheating is necessary when cast iron is welded by the oxyacetylene welding process. (4) In white cast iron. on machine tools as bases. Gray cast iron has low ductility and therefore will not expand or stretch to any considerable extent before breaking or cracking.7 percent and less than 4. The structure is changed to perlitic or ferritic. or other elements added to provide specific properties. which is used for abrasion resistance. (2) There are also alloy cast irons which contain small amounts of chromium. the cooling rate is increased and heat inputs may be extended about 25 percent. nickel. copper. (6) Nodular iron and ductile cast iron are made by the addition of magnesium or aluminum which will either tie up the carbon in a combined state or will give the free carbon a spherical or nodular shape. carbon. for pipe fittings and cast iron pipe. (7) Cast irons are widely used in agricultural equipment. in which the amount of carbon is usually more than 1. (5) Malleable cast iron is made by giving white cast iron a special annealing heat treatment to change the structure of the carbon in the iron. This butter weld bead must be located so that the toe of the fillet will be laid directly over it during actual fillet welding. Butter welding in the toe area before actual fillet welding strengths the area where a toe crack may start. (3) Another alloy iron is austenitic cast iron. It is widely used in construction machinery for counterweights and in other applications for which weight is required.

The color match can be a determining factor. can be welded without dismantling or preheating. By this procedure. such as motor blocks. different types of filler metal can be used. Welding is used to salvage new iron castings. and the danger of cracking the casting is eliminated. Special electrodes designed for this purpose are usually desirable.accomplished by welding only short lengths of the joint at a time and allowing these sections to cool. For example. can be successfully welded. where a difference of color would not be acceptable. and to join castings to each other or to steel parts in manufacturing operations. The filler metal will have an effect on the color match of the weld compared to the base material. malleable. the heat of welding is confined to a small area. when using the shielded metal arc welding process. to repair castings that have failed in service. The selection of the welding process and the welding filler metals depends on the type of weld properties desired and the service life that is expected. Large castings with complicated sections. and nodular irons.
. Ductile cast irons. such as malleable iron. Table 7-19 shows the welding processes that can be used for welding cast. specifically in the salvage or repair of castings. ductile iron. c. and nodular iron. these types of cast irons should be welded in the annealed condition. For best results.

e. The skin or high silicon surface should also be removed adjacent to the weld area on both the face and root side. it is best to assume that it is gray cast iron with little or no ductility. (3. oil. certain preparatory steps should be made. It is important to determine the exact type of cast iron to be welded. especially when heating and cooling vary over a range of temperatures exceeding 400°F (204°C). but the reliability and service life on such repairs cannot be predicted with accuracy. (2) Preheating is desirable for welding cast irons with any of the welding processes. Unless cast iron is used as the filler material. it is necessary to remove all surface materials to completely clean the casting in the area of the weld. The V should extend approximately 1/8 in. This means removing paint.d. A small hole should be drilled at each end of the crack to keep it from spreading. whether it is gray cast iron or a malleable or ductile type. No matter which of the welding processes is selected. (1) In preparing the casting for welding. grease. a V groove from a 60-90° included angle should be used. Preheating will reduce the thermal
. since a crack or defect not completely removed may quickly reappear under service conditions. it is not recommended to weld repair gray iron castings that are subject to heating and cooling in normal service. It can be reduced when using extremely ductile filler metal.2 mm) from the bottom of the crack. It is desirable to heat the weld area for a short time to remove entrapped gas from the weld zone of the base metal. Complete penetration welds should always be used. In general. The edges of a joint should be chipped out or ground to form a 60° angle or bevel. If exact information is not known. Preparation for Welding. the weld metal and base metal may have different coefficients of expansion and contraction. Repair of these types of castings can be made. and other foreign material from the weld zone. Where grooves are involved. This will contribute to internal stresses which cannot be withstood by gray cast iron.

gradient between the weld and the remainder of the cast iron.6 kg) or less. long (19. Preheat temperatures should be related to the welding process. (a) Cast iron can be welded with a coated steel electrode. the mass. and in some cases. Each weld metal deposit should be thoroughly cleaned before additional metal is added. Weaving of the electrode should be held to a minimum. (3) Slow cooling or post heating improves the machinability of the heat-affected zone in the cast iron adjacent to the weld.0 lb (13. Preheating should be general. temporary furnaces are built around the part rather than taking the part to a furnace.2 mm) in diameter to prevent excessive welding heat. This can be done by covering the casting with insulating materials to keep the air or breezes from it. it assists in degassing the casting.75 to 1. the arc should be struck in the V. the parts can be maintained at a high interpass temperature in the temporary furnace during welding. but this method should be used as an emergency measure only. f. by the backstep and skip procedure. and not on the surface of the base metal. Welding Technique. Torch heating is normally used for relatively small castings weighing 30. When using a steel electrode. this uneven shrinkage will cause strains at the joint after welding. Preheating can be done by any of the normal methods. To overcome these difficulties. and this in turn reduces the possibility of porosity of the deposited weld metal. To avoid hard spots. Preheating tends to help soften the area adjacent to the weld. the contraction of the steel weld metal. Larger parts may be furnace preheated. These are made intermittently and. the cast iron may crack just back of the line of fusion unless preventive steps are taken.0 to 25. since it helps to improve the ductility of the material and will spread shrinkage stresses over a large area to avoid critical stresses at any one point. and the hardness of the weld metal caused by rapid cooling must be considered. and allowed to cool before additional weld metal is applied.0 in. (3. The post cooling should be as slow as possible. (b) The electrodes used should be 1/8 in. and the complexity of the casting. and it increases welding speed. The peening action forges the metal and relieves the cooling strains. When a steel electrode is used. Stainless steel electrodes are used when machining of the weld is
. the prepared joint should be welded by depositing the weld metal in short string beads. Steel shrinks more than cast iron when ceded from a molten to a solid state. Each short length of weld metal applied to the joint should be lightly peened while hot with a small ball peen hammer. in some cases. When a large quantity of filler metal is applied to the joint. 0. (c) Cast iron electrodes must be used where subsequent machining of the welded joint is required. (1) Electrodes.4 mm). the filler metal type. Welding should be done with reverse polarity. the carbon picked up from the cast iron by the weld metal. In this way.

will help minimize dilution. playing the arc on the puddle rather than on the base metal. (d) There are three types of nickel electrodes used for welding cast iron. heating to 100°F (38°C) is recommended. if at all possible. Slow cooling after welding is recommended. In general. Zinc will volatilize in the arc and will cause weld metal porosity. These electrodes provide an excellent color match cm gray iron. which include the machinability of the deposit. (a) The shielded metal arc welding process can be utilized for welding cast iron. These electrodes can be used in all positions. A medium arc length should be used.not required. the strength of the deposit. and the ductility of the final weld. The arc should be directed against the deposited metal or puddle to avoid penetration and mixing the base metal with the weld metal. if necessary. postheating will improve
. (c) When the copper base electrodes are used. and peening will help reduce stresses and will minimize distortion. the color match of the deposit. Stainless steel electrodes provide excellent fusion between the filler and base metals. the flat position is recommended. The hardness of the heat-affected zone can be minimized by reducing penetration into the cast iron base metal. There are two types of copper-base electrodes: the copper tin alloy and the copper aluminum types. covered nickel base alloy electrodes. the easier it will be to machine the weld deposit. (b) When arc welding with the cast iron electrodes (ECI). (2) Arc Welding. preheat to between 250 and 800°F (121 and 425°C). The technique mentioned above. covered copper base alloy electrodes. Slow cooling and. The copper-base electrodes do not provide a good color match. welding should be done in the flat position. There are reasons for using each of the different specific types of electrodes. Wandering or skip welding procedure should be used. it is best to use small-size electrodes and a relatively 1ow current setting. however. however. The welding slag should be removed between passes. Small electrodes and low current should be used. The nickel and nickel iron deposits are extremely ductile and will not become brittle with the carbon pickup. contracts approximately 50 percent more than because stainless steel expands and mild steel in equal changes of temperature. and. Slow cooling is recommended after welding. There are four types of filler metals that may be used: cast iron covered electrodes. a preheat of 250 to 400°F (121 to 204°C) is recommended. The higher degree of heating. The copper zinc alloys cannot be used for arc welding electrodes because of the low boiling temperature of zinc. and mild steel covered electrodes. The procedure for making welds with these electrodes is the same as that outlined for welding with mild steel electrodes. Great care must be taken to avoid cracking in the weld. These electrodes can be used without preheat. The strength of the weld will equal the strength of the base metal. depending on the size and complexity of the casting and the need to machine the deposit and adjacent areas.

The optimum welding procedure should be used with regard to joint preparation. There are two classifications: a manganese bronze and a low-fuming bronze. This type of electrode should be used only for small repairs and should not be used when machining is required. The oxyfuel gas process is often used for welding cast iron. The flame should be neutral to slightly reducing. both are copper zinc alloys. and post heat. and the plasma arc can all be used as sources of heat. Either of these electrodes can be used in the same manner as the nickel or nickel iron electrode with about the same technique and results. The mild steel deposit will pick up sufficient carbon to make a high-carbon deposit. which is impossible to machine. The joint should be preheated by moving the carbon electrodes along the surface. (a) Brazing is used for joining cast iron to cast iron and steels. (e) Copper nickel type electrodes cane in two grades. the joint design must be selected for brazing so that capillary attraction causes the filler metal to flow between closely fitting parts. The nickel-base electrodes do not provide a close color match. This prevents too-rapid cooling after welding. Additionally. and a cast iron welding flux. and the weld should be peened as quickly as possible after welding. the carbon arc. Welds made with the proper cast iron electrode will be as strong as the base metal. Minimum preheat is possible for small repair jobs. Iron castings may be welded with a carbon arc. the mild steel deposit will have a reduced level of ductility as a result of increased carbon content.machinability of the heat-affected zone. Braze welding can also be used to join
. a cast iron rod. In these cases. the twin carbon arc. The mild steel electrode deposit provides a fair color match. preheat. Most of the fuel gases can be used. Two brazing filler metal alloys are normally used. (4) Oxyfuel gas welding. The welds are machinable. The copper zinc rods produce braze welds. The torch method is normally used. (f) Mild steel electrodes are not recommended for welding cast iron if the deposit is to be machined. The deposits of these electrodes do not provide a color match. Short welds using a wandering sequence should be used. Two types of filler metals are available: the cast iron rods and the copper zinc rods. In addition. (3) Carbon-arc welding of cast iron. Flux should be used. The deposited bronze has relatively high ductility but will not provide a color match. Small electrodes at low current are recommended to minimize dilution and to avoid the concentration of shrinkage stresses. The molten puddle of metal can be worked with the carbon electrode so as to move any slag or oxides that are formed to the surface. (5) Brazing and braze welding. Welds made with the carbon arc cool more slowly and are not as hard as those made with the metal arc and a cast iron electrode. Good color match is provided by all of these welding reds. the gas tungsten arc.

the deposited filler metal is extremely ductile. This electrode wire is normally operated with CO2 shielding gas.cast iron. Since there is little or no intermixing of the materials. (6) Gas metal arc welding. Several types of electrode wires can be used. Postheating is normally not required. This type of welding is commonly used for repair welding of automotive parts. a 200°F (93°C) preheat is sufficient for most application. High temperature preheating is not usually required for braze welding unless the part is extremely heavy or complex in geometry. In all cases. but when lower mechanical properties are not objectionable. (c) Silicon bronze using 50% argon + 50% helium for shielding. and even automotive engine blocks and heads. Braze welding will not provide a color match. small diameter electrode wire should be used at low current. the zone adjacent to the weld in the base metal is not appreciably hardened. This process has recently been used for welding cast irons. A color match is not obtained. the fracture is removed by grinding a V groove. (b) Braze welding can also be accomplished by the shielded metal arc and the gas metal arc welding processes. The cooling rate is not extremely critical and a stress relief heat treatment is not usually required. The weld and adjacent area are machinable after the weld is completed. In this process. the filler metal is not drawn into the joint by capillary attraction. A higher preheat is usually required to reduce residual stresses and cracking tendencies. (8) Studding. In braze welding. It can only be used when the absence of color match is not objectionable. This is sometimes called bronze welding. Holes are drilled and tapped
. which compensates for the lack of ductility of the cast iron. it can be operated without external shielding gas. The technique should minimize penetration into the cast iron base metal. The heat of the arc is sufficient to bring the surface of the cast iron up to a temperature at which the copper base filler metal alloy will make a bond to the cast iron. The more successful application has been using a nickel base flux-cored wire. agricultural implement parts. (b) Nickel copper using 100% argon for shielding. 7-10). Cracks in large castings are sometimes repaired by studding (fig. With the mild steel electrode wire. The minimum preheat temperatures can be used. (7) Flux-cored arc welding. the Argon-CO2 shielding gas mixture issued to minimize penetration. In the case of the nickel base filler metal and the Copper base filler metal. The bronze weld metal deposit has extremely high ductility. including: (a) Mild steel using 75% argon + 25% CO2 for shielding. The gas metal arc welding process can be used for making welds between malleable iron and carbon steels. The mild steel provides a fair color match. In general. The filler material having a liquidous above 850°F (454°C) should be used.

excessive expansion and distortion of the metal are prevented. The studs should be seal welded in place by one or two beads around each stud. ALUMINUM WELDING a. and studs are screwed into these holes for a distance equal to the diameter of the studs.4 mm) above the cast iron surface. If the studding method cannot be applied. Aluminum gives off no sparks in a spark test. (6. A heavy film of white oxide forms instantly on the molten surface. Each bead should be allowed to cool and be thoroughly cleaned before additional metal is deposited. Welds should be made in short lengths. A fracture in aluminum sections shows a smooth. machined. very bright when polished. it is suitable only in low temperature applications. General. Aluminum is a lightweight. shown by table 7-20. low strength metal which can easily be cast. with the upper ends projecting approximately 1/4 in.. Unless alloyed with specific elements. This system of alloy groups.at an angle on each side of the groove. It is important to know which alloy is to be welded. Its combination of light weight and high strength make aluminum the second most popular metal that is welded.
Section IV. formed and welded. Aluminum is light gray to silver in color. Aluminum and aluminum alloys can be satisfactorily welded by metal-arc. carbon-arc. and dull when oxidized. Many alloys of aluminum have been developed. to designate the various wrought aluminum alloy types. and is sometimes used for repairing small defects in small castings. Inc. Alloys. and each length peened while hot to prevent high stresses or cracking upon cooling. Flash welding can also be used for welding cast iron. b. and other arc welding processes. For this reason. The principal advantage of using arc welding processes is that a highly concentrated heating zone is obtained with the arc. forged. and does not show red prior to melting. is as follows:
. soft. bright structure. Soldering can be used for joining cast iron. GENERAL DESCRIPTION AND WELDABILITY OF NONFERROUS METALS
7-17. the edges of the joint should be chipped out or machined with a round-nosed tool to form a U groove into which the weld metal should be deposited. Thermit welding has been used for repairing certain types of cast iron machine tool parts. A system of four-digit numbers has been developed by the Aluminum Association. and then tied together by weld metal beads.
(9) Other welding processes can be used for cast iron.

Manganese is the major alloying element in this group. which provides extremely high strength when properly heat treated. Most of the alloys in this group are non-heat-treatable. (1) Aluminum is an active metal which reacts with oxygen in the air to produce a hard.5 percent. Aluminum possesses a number of properties that make welding it different than the welding of steels. (6) 6XXX series. (7) 7XXX series.(1) 1XXX series. (5) 5XXX series. They possess good welding characteristics and good resistance to corrosion. These are aluminums of 99 percent or higher purity which are used primarily in the electrical and chemical industries. which is nonheat-treatable. These alloys possess medium strength and good corrosion resistance. The normal metallurgical factors that apply to other metals apply to aluminum as well. The melting point of aluminum oxide is approximately 3600°F (1982°C) which is almost three times the melting point of pure
. These are: aluminum oxide surface coating. high thermal conductivity. Copper is the principal alloy in this group. Zinc is the major alloying element in this group. Magnesium is the major alloying element of this group. These alloys are used in the aircraft industry. Welding Aluminum Alloys. It can be added in sufficient quantities to substantially reduce the melting point and is used for brazing alloys and welding electrodes. (4) 4XXX series. These alloys have moderate strength and are easily worked. but the amount of cold work should be limited. high thermal expansion coefficient. which are alloys of medium strength. Together. Alloys in this group contain silicon and magnesium. Silicon is the major alloying element in this group. Manganese content is limited to about 1. (2) 2XXX series. they form a heat-treatable alloy of very high strength. which is used for aircraft frames. and the absence of color change as temperature approaches the melting point. Magnesium is also included in most of these alloys. thin film of aluminum oxide on the surface. (3) 3XXX series. These alloys do not produce as good corrosion resistance and are often clad with pure aluminum or special-alloy aluminum. which make them heat treatable. low melting temperature. c.

(b) The aluminum oxide can be removed by mechanical. sandpaper. paint. free hydrogen is retained within the weld and will cause porosity. lack of fusion. the flux and alkaline etching materials must be completely removed from the weld area to avoid future corrosion. CAUTION Aluminum and aluminum alloys should not be cleaned with caustic soda or cleaners with a pH above 10. hot and cold rinsing is highly recommended. but must be used with care. as well as from the base metal. One is by use of cleaning solutions. and possibly weld cracking.aluminum (1220°F (660°C)). It also comes from the oxide and foreign materials on the electrode or filler wire. This is an electrical phenomenon that actually blasts away the oxide coating to produce a clean surface. wire brush (stainless steel). The nonetching types should be used only when starting with relatively clean parts. Cathodic bombardment occurs during the half cycle of alternating current gas tungsten arc welding when the electrode is positive (reverse polarity). chemical. The time in the solution must be controlled so that too much etching does not occur. and are used in conjunction with other solvent cleaners. In addition. and dirt in the weld area. If it is not completely removed. The time of buildup is not extremely fast. the etching type solutions are recommended. it will retain much less hydrogen. small particles of unmelted oxide will be trapped in the weld pool and will cause a reduction in ductility. filing. and soldering. Mechanical removal involves scraping with a sharp tool. as they may react chemically. As the aluminum solidifies. this aluminum oxide film absorbs moisture from the air. (c) Chemical cleaning includes the use of welding fluxes. the oxide film will immediately start to reform. The coating on covered aluminum electrodes also maintains fluxes for cleaning the base metal. depending on the amount. Fluxes are used for gas welding. For better cleaning. Chemical removal can be done in two ways. The hydrogen is rejected during solidification. brazing. or any other mechanical method. (a) The aluminum oxide film must be removed prior to welding. Whenever etch cleaning or flux cleaning is used. but welds should be made
. Porosity will decrease weld strength and ductility. particularly as it becomes thicker. which causes porosity in aluminum welds. The etching type solutions are alkaline solutions. With a rapid cooling rate. or electrical means. This is one of the reasons why AC gas tungsten arc welding is so popular for welding aluminum. either the etching types or the nonetching types. Hydrogen will enter the weld pool and is soluble in molten aluminum. When dipping is employed. Hydrogen may also come from oil. Moisture is a source of hydrogen. (d) The electrical oxide removal system uses cathodic bombardment. (e) Since aluminum is so active chemically.

(3. aluminum welds decrease about 6 percent in volume when solidifying from the molten state. Along with surface tension.5 mm) thick. (3. More heat must be put into the aluminum. flux is used. even though the melting temperature of aluminum is less than half that of steel. Because of the difficulty of controlling the arc. The flux will melt as the temperature of the base metal approaches the temperature required. This weld may be porous and unsuitable for liquid-or gas-tight joints. The polarity to be used should be determined by trial on the joints to be made. In addition. (63. particularly suitable for heavy material and is used on plates up to 2-1/2 in. depending on the specific alloy. When torch welding with oxyacetylene or oxyhydrogen. This change in dimension may cause distortion and cracking. because the weld is completed before the adjoining area melts. a joint prepared with a 20 degree bevel will have strength equal to a weld made by the oxyacetylene process. (3) The thermal expansion of aluminum is twice that of steel. When soldering or brazing aluminum with a torch. The high heat conductivity of aluminum can be helpful. The current and polarity settings will vary with each manufacturer's type of electrodes. since the weld will solidify very quickly if heat is conducted away from the weld extremely fast. (1) Plate welding. Both the gas tungsten arc and the gas metal arc processes supply this requirement. d. color is not as important.2 mm). It conducts heat three to five times as fast as steel. and the parts should not be held at that temperature longer than necessary. procedures should utilize higher speed welding processes using high heat input. weld joint strength in both heat-treated and work-hardened alloys may be diminished. butt and fillet welds are difficult to produce in plates less than 1/8 in. (This aids in knowing when welding temperatures are reached. If the temperature is too high or the time period is too long.2 mm) thick.
. and melts as the base metal reaches the correct working temperature. at which time it will glow a dull red. When welding plate heavier than 1/8 in. preheat is often used for welding thicker sections. (2) Aluminum has a high thermal conductivity and low melting temperature. the surface of the base metal will melt first and assume a characteristic wet and shiny appearance. The preheat for aluminum should not exceed 400°F (204°C). Metal-arc welding is. The flux dries out first. Because of the high thermal conductivity. Metal-Arc Welding of Aluminum. however.) When welding with gas tungsten arc or gas metal arc. this helps hold the weld metal in position and makes all-position welding with gas tungsten arc and gas metal arc welding practical.after aluminum is cleaned within at least 8 hours for quality welding. Because of the high heat conductivity. If a longer time period occurs. the quality of the weld will decrease. (2) Current and polarity settings. (4) The final reason aluminum is different from steels when welding is that it does not exhibit color as it approaches its melting temperature until it is raised above the melting point.

This fast. At a specific current and arc length. This requires adding a relatively large amount of filler alloy to fill the groove. in any position. because of the higher fluidity of aluminum under the welding arc. With the lighter gauges of aluminum sheet. The effectiveness of this particular design depends upon surface tension. helium provides deeper penetration and a hotter arc than argon. Arc voltage is higher with helium. (3. Excellent control of the penetration and sound root pass welds are obtained. Argon produces a smother and more stable arc than helium.2 mm) thick. A specially designed V groove that is applicable to aluminum is shown in A. less groove spacing is advantageous when weld dilution is not a factor. and a given change in arc length results in a greater change
.
e. penetrating bead is desired. adaptable process is used with direct current re-verse polarity and an inert gas to weld heavier thicknesses of aluminum alloys. (1.6 mm) to several inches thick. It eliminates difficulties due to burn-through or over-penetration in the overheat and horizontal welding positions. The controlling factor is joint preparation. This edge preparation can be employed for welding in all positions.(3) Plate edge preparation. TM 5-3431-211-15 describes the operation of a typical MIG welding set. the design of welded joints for aluminum is quite consistent with that for steel joints. and should be applied on all material over 1/8 in. Welding grade argon. figure 7-11. This type of joint is excellent where welding can be done from one side only and where a smooth. In general. helium. or a mixture of these gases is used for aluminum welding. The bottom of the special V groove must be wide enough to contain the root pass completely. However. from 1/016 in. some important general principles should be kept in mind. Precautions should be taken to ensure the gas shield is extremely efficient. (1) General. It is applicable to all weldable base alloys and all filler alloys. (2) Shielding gas. Gas Metal-Arc (MIG) Welding (GMAW).

The angle of the gun or torch is more critical when welding aluminum with inert shielding gas.
. The electrode wire tip should be oversize for aluminum. The bead profile and penetration pattern of aluminum welds made with argon and helium differ. The penetration pattern shows a deep central section. A 30° leading travel angle is recommended. A mixture of approximately 75 percent helium and 25 percent argon provides the advantages of both shielding gases with none of the undesirable characteristics of either. wider bead. With argon.in arc voltage. Table 7-21 provides welding procedure schedules for gas metal-arc welding of aluminum. the bead profile is narrower and more convex than helium. Arc stability is comparable to argon. and has a broader under-bead penetration pattern. Penetration pattern and bead contour show the characteristics of both gases. Helium results in a flatter.

.

Watercooled guns are required except for low-current welding.
. the welder moves the electrode along the joint while maintaining a 70 to 85 degree forehand angle relative to the work. A slight backhand angle is sometimes helpful when welding thin sections to thick sections. reverse the direction of travel. In addition. The electrode wire must be clean. Edges may be prepared for welding by sawing. A string bead technique is normally preferred. Arc travel speed controls the bead size.0 in. For this reason. When welding thick plates to thin plates. When finishing or terminating the weld. and proceed with normal welding. Runoff tabs are commonly used. the CV system is preferred when welding on thin material and using all diameter electrode wire. best results are obtained by pointing the gun slightly upward. The constant current power source with a moderate drop of 15 to 20 volts per 100 amperes and a constant speed wire feeder provide the most stable power input to the weld and the highest weld quality. rotary planing. In general. a similar practice may be followed by reversing the direction of welding. Care should be taken that the forehand angle is not changed or increased as the end of the weld is approached. When welding aluminum with this process.4 mm) ahead of the beginning of the weld and then quickly bring the arc to the weld starting point. (4) Joint design. the constant speed wire feeder is sometimes used with the constant current power source. Having established the arc. The wire feeding equipment for aluminum welding must be in good adjustment for efficient wire feeding. It is more difficult to push extremely small diameter aluminum wires through long gun cable assemblies than steel wires. The weld quality seems better with this system. it is helpful to direct the arc toward the heavier section. The arc is struck with the electrode wire protruding about 1/2 in. The root pass of a joint usually requires a short arc to provide the desired penetration. Use nylon type liners in cable assemblies. When welding uniform thicknesses.7 mm) from the cup. Acceptable joint designs are shown in figure 7-12. A frequently used technique is to strike the arc approximately 1. the arc may be struck outside the weld groove on a starting tab. it is must important that high travel speeds be maintained. When welding in the horizontal position. This helps to avert craters and crater cracking. Both the constant current (CC) power source with matching voltage sensing wire feeder and the constant voltage (CV) power source with constant speed wire feeder are used for welding aluminum. the electrode to work angle should be equal on both sides of the weld. (12. It provides better arc starting and regulation. and simultaneously increasing the speed of welding to taper the width of the molten pool prior to breaking the arc.(3) Welding technique. Proper drive rolls must be selected for the aluminum wire and for the size of the electrode wire. Slightly longer arcs and higher arc voltages may be used on subsequent passes. the spool gun or the newly developed guns which contain a linear feed motor are used for the small diameter electrode wires. The CC system is preferred when welding thick material using larger electrode wires. machining. Alternatively. (25. routing or arc cutting.

There are several precautions that should be mentioned with respect to using this process.f. (1) The gas tungsten arc welding process is used for welding the thinner sections of aluminum and aluminum alloys. Gas Tungsten-Arc (TIG) Welding (GTAW). Table 7-22 provides welding procedure schedules for using the process on different thicknesses to produce different
. (a) Alternating current is recommended for general-purpose work since it provides the half-cycle of cleaning action.

it must be redressed. Procedures should be followed closely and special attention given to the type of tungsten electrode. If it does accidentally touch the molten metal. When manual welding. and gas flow rates.
. The tungsten electrode should not protrude too far beyond the end of the nozzle. AC welding. gas type. usually with high frequency. The tungsten electrode should be kept clean.welds. the arc length should be kept short and equal to the diameter of the electrode. is widely used with manual and automatic applications. size of welding nozzle.

.

(c) For automatic or machine welding.
. When dc electrode negative is used. and pulsing. extremely deep penetration and high speeds can be obtained. Cleaning must be extremely efficient.(b) Welding power sources designed for the gas tungsten arc welding process should be used. pre-and postflow of shielding gas. direct current electrode negative (straight polarity) can be used. since there is no cathodic bombardment to assist. Table 7-23 lists welding procedure schedules for dc electrode negative welding. The newer equipment provides for programming.

.

and attraction of added filler metal to the weld puddle rather than a tendency to repulsion. The joint designs shown in figure 7-11 are applicable to the gas tungsten-arc welding process with minor exceptions. Both hands are moved in unison with a slight backward and forward motion along the joint. One rule is to use an arc length approximately equal to the diameter of the tungsten electrode. quickly break and restrike the arc several times while adding additional filler metal to the crater. The tungsten electrode should not touch the filler rod. or use a foot control to reduce the current at the end of the weld. or a mixture of the two. Argon is used at a lower flow rate. Inexperienced welders who cannot maintain a very short arc may require a wider edge preparation. included angle.(d) The shielding gases are argon. (b) Welding technique. Tacking before welding is helpful in controlling distortion. or joint spacing. A stable arc results in fewer tungsten inclusions. The welding of aluminum by the gas tungsten-arc welding process using alternating current produces an oxide cleaning action. A short arc length must be maintained to obtain sufficient penetration and avoid undercutting. When the arc is broken. helium. (2) Alternating current. For manual welding of aluminum with ac. When filler wire is used. This technique reduces the tendency for tungsten inclusions at the start of the weld. (a) Characteristics of process. it must be clean. shrinkage cracks may occur in the weld crater. The hot end of the filler rod should not be withdrawn from the argon shield. but a higher flow rate is required. the electrode holder is held in one hand and filler rod. If filler metal is required. and consequent loss of penetration control and weld contour. The arc is then broken and reignited in the joint. smooth arc starting. excessive width of the weld bead. resulting in a defective weld. (c) Joint design. Argon shielding gas is used. An initial arc is struck on a starting block to heat the electrode. Better results are obtained when welding aluminum with alternating current by using equipment designed to produce a balanced wave or equal current in both directions. Tack welds should be of ample size and strength and should be chipped out or tapered at the ends before welding over. Characteristics of a stable arc are the absence of snapping or cracking. Helium increases penetration. The establishment and maintenance of a suitable weld pool is important. Oxide not removed from the filler wire may include moisture that will produce polarity in the weld deposit. Edge
. Joints may be fused with this process without the addition of filler metal if the base metal alloy also makes a satisfactory filler alloy. The arc is held at the starting point until the metal liquefies and a weld pool is established. and welding must not proceed ahead of the puddle. in the other. Then. Unbalance will result in loss of power and a reduction in the cleaning action of the arc. it may be added to the front or leading edge of the pool but to one side of the center line. if used. This defect can be prevented by gradually lengthening the arc while adding filler metal to the crater.

the crater should be filled to a point above the weld bead to eliminate crater cracks. there are the advantages of surface cleaning produced by positive ionic bombardment during the reversed polarity cycle. (1) General. or laid on the joint and melted as the arc roves forward. This process. which is consequently deeper and narrower. Root face can be thicker. the time of current flow in either direction is adjustable from 20 to 1. for adjusting the current as the work heats. (c) Joint designs.and corner welds are rapidly made without addition of filler metal and have a good appearance. since melting occurs the instant the arc is struck. Since there is less tendency to heat the electrode. and the heat affected zone will be smaller with less distortion. The use of direct current straight polarity (dcsp) provides a greater heat input than can be obtained with ac current. The joint designs shown in figure 7-11 are applicable to the automatic gas tungsten-arc dcsp welding process with minor exceptions. In square wave gas tungsten-arc welding. but a very close fit is essential. especially in the welding of heavy sections. (b) Welding techniques. and build up can be easily controlled by varying filler wire size and travel speed. Square wave gas tungsten-arc welding with alternating current differs frozen conventional balanced wave gas tungsten-arc welding in the type of wave from used. A high frequency current should be used to initiate the arc. In dcsp welding. The fillet size can be controlled by varying filler wire size. Greater heat is developed in the weld pool. (3) Direct current straight polarity. g. Sufficient aluminum surface cleaning action has
. It is not necessary to form a puddle as in ac welding. The filler wire is fed evenly into the leading edge of the weld puddle. Square Wave Alternating Current Welding (TIG). using helium and thoriated tungsten electrodes is advantageous for many automatic welding operations. These are helpful in preventing or filling craters. (a) Charcteristics of process. the concentrated heat of the arc gives excellent root fusion. grooves narrower. Preheat is not required even for heavy sections. This will contribute to keeping the weld bead narrow. smaller electrodes can be used for a given welding current. and to adjust for a change in section thickness. Standard techniques such as runoff tabs and foot operated heat controls are used. With a square wave. In all cases. Touch starting will contaminate the tungsten electrode. DCSP is adaptable to repair work. along with greater weld depth to width ratio produced by the straight polarity cycle. For manual dcsp. Care should be taken to strike the arc within the weld area to prevent undesirable marking of the material. the torch is moved steadily forward.

The electrodes are covered similarly to conventional steel electrodes. depending on the application to be used. a heavy dipped or extruded flux coated electrode is used with dcrp. erratic arc control. The process can be either manual or automatic with procedures and techniques closely related to those used in oxyacetylene welding. j. along with favorable welding residual stress distribution and less use of filler wire. Visibility is increased. and must be restarted each tire.5 mm). k. Manual shielded carbon-arc welding is usually limited to a thickness of less than 3/8 in.
. smaller amounts of flux are required to combine or remove aluminum oxide. (3) Joint design.been obtained with a setting of approximately 10 percent dcrp. Flux must be removed after welding. Since the hydrogen shield surrounding the base metal excludes oxygen. helium. Smaller V grooves. With Some slight modification. In the shielded metal-arc welding process. U grooves. and structure as those produced by either oxyacetylene or oxyhydrogen welding. Square wave alternating current welding offers substantial savings over conventional alternating current balanced wave gas tungsten arc welding in weld joint preparation. soundness. When welding aluminum. Stud Welding. because the arc is extinguished every half cycle as the current decays toward zero. the same joint designs can be used as in dcsp gas tungsten-arc welding (fig. there are fewer flux inclusions. A carbon arc is used as a source of heat while filler metal is supplied from a separate filler rod. the process is rather limited due to arc spatter. accomplished by the same method used for manual carbon arc welding of other material. 7-11). Joint preparation is similar to that used for gas welding. Argon. It is necessary to have either superimposed high frequency or high open circuit voltage. A flux covered rod is used. Atomic Hydrogen Welding. or a combination of the two should be used as shielding gas. limitations on thin material. and a thicker root face can be used. (9. and the corrosive action of the flux if it is not removed properly. i. Penetration equal to regular dcsp welding can be obtained with 90 percent dcsp current. A greater depth to width weld ratio is conducive to less weldment distortion. Shielded Metal-Arc Welding. Shielded carbon-arc welding is done both manually and automatically. It requires flux and produces welds of the same appearance. The flux coating provides a gaseous shield around the arc and molten aluminum puddle. and a very sound metal is deposited. This welding process consists of maintaining an arc between two tungsten electrodes in an atmosphere of hydrogen gas. forming a slag. otherwise severe corrosion will result. The shielded carbon-arc welding process can be used in joining aluminum. Shielded Carbon-Arc Welding. and chemically combines and removes the aluminum oxide. h. Precision shaped thoriated tungsten electrodes should be used with this process. (2) Welding technique.

(1.0 mm) diameter.6 to 6. The electron beam is capable of such intense local heating that it almost instantly vaporizes a hole through the entire joint thickness. Electron Beam Welding. (4. The conventional arc stud welding process may be used to weld aluminum studs 3/16 to 3/4 in. A small cylindrical or cone shaped projection on the end of the aluminum stud initiates the arc and helps establish the longer arc length required for aluminum welding. using either the capacitor discharge or drawn arc capacitor discharge techniques. in which the weld energy is stored at a low voltage in capacitors with high capacitance as a power source. In the capacitor discharge stud welding process. It does not require a serrated tip or projection on the end of the stud for arc initiation.4 mm) diameter. and as the hole is moved along the joint. Resistance Welding. However. use of the projection on the base of the stud provides the most consistent welding. The short arcing time of the capacitor discharge process limits the melting so that shallow penetration of the workpiece results.
. l. This flaws around the bore of the hole and solidifies along the rear side of the hole to make the weld. Further penetration comes solely by conduction of heat in all directions from this molten surface spot. The aluminum stud welding gun is modified slightly by the addition of a special adapter for the control of the high purity shielding gases used during the welding cycle. melt-thru lap. Electron beam welding is a fusion joining process in which the workpiece is bombarded with a dense stream of high velocity electrons. (0.800 mm). Filler metal is rarely used except for surfacing. fillet. with the electrode gun positive and the workpiece negative.7 to 19.(1) Aluminum stud welding may be accomplished with conventional arc stud welding equipment. more metal on the advancing side of the hole is melted. and virtually all of the kinetic energy of the electrons is transformed into heat upon impact. Electron beam welding usually takes place in an evacuated chamber. Conventional arc and gas heating melt little more than the surface. An added accessory control for controlling the plunging of the stud at the completion of the weld cycle adds materially to the quality of weld and reduces spatter loss.032 in. The walls of this hole are molten. The chamber size is the limiting factor on the weldment size. Electron beam welding is generally applicable to edge. and spot welds. The minimum aluminum work thickness considered practical is 0. Capacitor discharge welding uses a low voltage electrostatic storage system. m. butt. The intensity of the beam can be diminished to give a partial penetration with the same narrow configuration. a small tip or projection on the end of the stud is used for arc initiation. In both cases. The drawn arc capacitor discharge stud welding process uses a stud with a pointed or slightly rounded end. The fusion zone widens as it depends. the weld cycle is similar to the conventional stud welding process. Reverse polarity is used. (2) The unshielded capacitor discharge or drawn arc capacitor discharge stud welding processes are used with aluminum studs 1/16 to 1/4 in.

Aluminum can also be
. Spot welds should always be designed to carry shear loads. it is usually necessary to reduce this oxide coating prior to welding. which are difficult to join by fusion welding. or identification markings. Welds of uniformly high strength and good appearance depend upon a consistently low surface resistance between the workplaces. but can be joined by the resistance welding process with practically no loss in strength. special tests should be conducted to determine the actual strength of the joint under service loading. except that the electrodes are replaced by wheels. seam. The resistance welding processes (spot. The joints so produced fail outside of the weld area when tension loads are applied. when tension or combined loadings may be expected. This process is particularly adapted to making butt or miter joints between two parts of similar cross section. Satisfactory performance of spot welds in service depends to a great extent upon joint design. the seam welding machine can produce uniformly spaced spot welds equal in quality to those produced on a regular spot welding machine. All aluminum alloys may be joined by the flash welding process. Electroslag welding. and cold welding are used for aluminums. The spots made by a seam welding machine can be overlapped to form a gas or liquid tight joint. Surface preparation for welding generally consists of removal of grease. By adjusting the timing. an absolutely neutral flame is required. ultrasonic welding. Gas welding has been done on aluminum using both oxyacetylene and oxyhydrogen flames. Submerged arc welding has been used in some countries where inert gas is not available. Electroslag welding is used for joining pure aluminum. some cleaning operations are necessary before spot or seam welding aluminum.(1) General. In either case. For most applications. Seam welding of aluminum and its alloys is very similar to spot welding. It has been adapted to joining aluminum to copper in the form of bars and tubing. Other processes. The process also is not too popular because of low heat input and the need to remove flux. This procedure is called roll spot or intermittent seam welding. including friction welding. p. Most of the solid state welding processes. but is not successful for welding the aluminum alloys. To obtain spot or seam welds of the highest strength and consistency. Gas welding. n. The natural oxide coating on aluminum has a rather high and erratic electrical resistance. and reduction and improvement of consistency of the oxide film on the aluminum surface. (2) Spot welding. These processes are especially useful in joining the high strength heat treatable alloys. The strength of spot welds in direct tension may vary from 20 to 90 percent of the shear strength. However. dirt. oil. (3) Seam welding. (4) Flash welding. and flash welding) are important in fabricating aluminum alloys. o. Flux is used as well as a filler rod. and at a faster rate.

However. General. High brasses contain from 20 to 45 percent zinc. welding is accomplished in much the same way the bronze is bonded to steel. Brasses and bronzes can be successfully welded by the metal-arc process. This process is particularly suited for piping because it can be done in all welding positions. d. e. Tensile strength. As with gas metal arc welding. and bronze has tin as the major alloying elements. Brasses can be welded with phosphor bronze. and some contain zinc and no tin at all. the weld metal should be deposited with a weave approximately three times the width of the electrode.
. Brass has zinc. For oxyacetylene welding of the high brasses. Stringer beads should be used. Brazing can be accomplished by most brazing methods. This method can be used to weld brasses and bronzes with filler reds of approximately the same composition as the base metal. 7-18. Silicon copper welding rods or one of the brass welding rods may be used. All welding should be done in the flat position. and ductility increase as the percentage of zinc increases. otherwise the zinc content will be volatilized. A flux is required. The metal should be preheated to the 350 to 400°F (177 to 204°C) range. low-fuming welding rods are used. A high silicon alloy filler material is used. c. f. electrode positive. If possible. Preheating and an auxiliary heat source may also be necessary. Direct current. The metal in the carbon arc is superheated. Backing plates of matching metal or copper should be used. hardness. The molten weld pool should be kept small and the travel speed rather high. aluminum bronze. In this process. Gas Metal Arc Welding. The low brasses are readily jointed by oxyacetylene welding. Either stabilized ac or direct current. The electrode used should be of the shielded arc type with straight polarity (electrode positive). or silicon bronze electrodes. and the travel speed should be as fast as practical. These low-fuming rods have composition similar to many of the high brasses. Carbon-Arc Welding. hot peening of each layer of weld metal is beneficial. Brass and bronze are alloys of copper. These metals are suitable for both hot and cold working. Oxyacetylene Welding. BRASS AND BRONZE WELDING a. electrode negative can be used with helium or argon shielding. b. Gas tungsten arc welding is used primarily for repair of castings and joining of phosphor bronze sheet. High welding current should not be used for welding copperzinc alloys (brasses). and this very hot metal is alloyed to the base metal in the joint. Metal-Arc Welding. and the torch flame should be adjusted to a slightly oxidizing flame to assist in controlling fuming. Gas Tungsten Arc Welding. Hot peening of each layer will reduce welding stresses and the likelihood of cracking. The welding procedures for copper are also suitable for the brasses.joined by soldering and brazing. Gas metal arc welding is recommended for joining large phosphor bronze fabrications and thick sections. some bronze metals contain more zinc than tin. and argon shielding are normally used. depending on the base metal composition and the service required.

particularly if the weld metal is to be cold worked. Copper shares some of the characteristics of aluminum. Postweld annealing at 900°F (482°C) is not always necessary. The melting point of the different copper alloys varies over a relatively wide ranger but is at least 1000°F (538°C) lower than carbon steel. Phosphor bronze covered electrodes are available for joining bronzes of similar compositions. to an even greater degree. must be strictly avoided. Shielded Metal Arc Welding. Copper and copper-base alloys have specific properties which make them widely used. but lower than aluminum.g. These are: (1) High thermal conductivity. The oxygen free copper can be welded with more uniform results than the oxygen bearing copper. Copper alloys are also widely used for friction or bearing applications. (4) Hot short or brittle at elevated temperatures. Copper can be welded satisfactorily with either bare or coated electrodes. Baking the electrodes at 250 to 300°F (121 to 149°C) before use may be necessary to reduce moisture in the covering to an acceptable level. and preheating of the base metal is necessary. COPPER WELDING a. but is desirable for maximum ductility. Due to the high thermal conductivity of copper. Their high electrical conductivity makes them widely used in the electrical industries. These electrodes are designed for use with direct current. both on the work and in the electrode coverings. and corrosion resistance of certain alloys makes them very useful in the process industries. Some of the copper alloys are hot short. 7-19. (2) High thermal expansion coefficient. which tends to become brittle when welded. (6) High electrical conductivity. approximately 50 percent higher than carbon steel. (3) Relatively low melting point. electrode positive. Filler metal should be deposited as stringer beads for best weld joint mechanical properties. Copper has a relatively high coefficient of thermal expansion. General. and the comments made concerning thermal conductivity of aluminum apply to copper. Moisture. Copper alloys possess properties that require special attention when welding. (5) Very fluid molten metal. Copper has the highest thermal conductivity of all commercial metals. (7) Strength due to cold working. This means
. Attention should be given to its properties that make the welding of copper and copper alloys different from the welding of carbon steels. the welding currents are higher than those required for steel. but is weldable.

and when it melts it is relatively fluid. The copper silicon filler wires are used with this material.that they become brittle at high temperatures. preheat should be used and can run from 250 to 1000°F (121 to 538°C). The heat of welding will anneal the copper in the heat-affected area adjacent to the weld. (2) Metal-arc welding of copper differs from steel welding as indicated below:
. The deoxidized coppers are preferred because of their freedom from embrittlement by hydrogen. The oxygen-free high-conductivity copper contains no oxygen and is not subject to grain boundary migration. This is essentially the result of the high preheat normally used for heavier sections. The entrapped high temperature water vapor or steam can create sufficient pressure to cause cracking. In common with all copper welding. since too much heat or slow welding can contribute to oxidation. Copper has the highest electrical conductivity of any of the commercial metals. All of the copper alloys derive their strength from cold working. The tough pitch electrolytic copper is difficult to weld because of the presence of copper oxide within the material.88 percent or higher and some high copper alloys which have 96. electrode positive. embrittling the material. During welding. There are three basic groups of copper designations.95 percent or higher. and usually results in less distortion. Hydrogen embrittlement occurs when copper oxide is exposed to a reducing gas at high temperature. The first is the oxygen-free type which has a copper analysis of 99. The second subgroup are the tough pitch coppers which have a copper composition of 99. It is faster. Welds should be made as quickly as possible. The preheat temperatures needed to make the weld quickly apply to all three grades. The gas-shielded processes are recommended since the welding area is more localized and the copper oxide is less able to migrate in appreciable quantities. Copper does not exhibit heat colors like steel. the copper oxide will migrate to the grain boundaries at high temperatures. It can produce highquality welds in all positions. and reduce the strength provided by cold working. depending on the mass involved. which reduces ductility and tensile strength. It uses direct current. Gas Metal-Arc (MIG) Welding (GMAW). This must be considered when welding high-strength joints. The CV type power source is recommended. (1) The gas metal arc welding process is used for welding thicker materials.00 percent or more copper. has a higher deposition rate. because some of the alloying elements form oxides and other compounds at the grain boundaries. Adequate gas coverage should he used to avoid oxygen of the air caning into contact with the molten metal. The hydrogen reduces the copper oxide to copper and water vapor. c. The third copper subgroup is the high-copper alloys which may contain deoxidizers such as phosphorus. This is a definite problem in the resistance welding processes.

13 cm) thick. (d) Higher preheat and interpass temperatures are required (800°F (427°C) for copper. (1) Copper can be successfully welded by the gas tungsten-arc welding process. (4) Peening is used to reduce stresses in the joints. although it can be used for welding oxygen-bearing copper up to 3/8 in. because vigorous blows could cause crystallizations or other defects in the joint. The weldability of each copper alloy group by this process depends upon the alloying elements used. For this reason. More frequent tack welds should be used. Numerous moderate blows should be used. (9. The root opening for thinner material should be 3/16 in. Flat-nosed tools are used for this purpose.05 in. (e) Higher currents are required for a given size electrode or plate thickness. slag inclusions. high frequency alternating current or direct current reverse polarity is used for beryllium copper or copper alloy sheets less than 0. (c) Larger groove angles are required. Electrodes for use with alternating currents are available. and porosity. a flux is recommended.5 mm) for heavier material. no one set of welding conditions will cover all groups. However. Gas Tungsten-Arc (TIG) Welding (GTAW). The electrode should be graphite type carbon. (3) Most copper and copper alloy coated electrodes are designed for use with reverse (electrode positive) polarity. and 3/8 in. d. a flux containing fluoride should never be used since the arc will vaporize the fluoride and irritate the lungs of the operator. in order to avoid excessive undercutting. CAUTION Never use a flux containing fluoride when welding copper or copper alloys. Carbon-Arc Welding. (3) For some copper alloys.(a) Greater root openings are required. (b) Tight joints should be avoided in light sections. (4. e. 700°F (371°C) for beryllium copper).5 mm) in thickness. Phosphor bronze welding rods are used most frequently in this process. sharpened to a long tapered point at least equal to the size of the welding rod. (0. (2) Direct current straight polarity is generally used for welding most copper alloys. However. (9.8 mm). particularly in heavy sections.
. (1) This process for copper welding is most satisfactory for oxygen-free copper.

which can result in weld cracking. must be removed from the surface prior to welding. c. containing small amounts of thorium. These are: (1) Magnesium oxide surface coating which increases with an increase in temperature. (3) Relatively high thermal expansion coefficient. such as aluminum. Aluminum added as an alloy up to 10 percent improves weldability. along with other foreign matter and metallic oxides. Many of these are the same as for aluminum. even at the start. possesses excellent welding qualities and freedom from cracking Weldments of these alloys do not require stress relieving. Magnesium possesses properties that make welding it different from the welding of steels. Certain magnesium alloys are subject to stress corrosion. to obtain desired properties. Cleaning. d. A final bright chrome pickle finish is
. the strength of the heat-affected zone may be reduced slightly. Mechanical cleaning can be utilized if chemical cleaning facilities are not available. since it tends to refine the weld grain structure. corrosion resistant.(2) The arc should be sharp and directed entirely on the weld metal. Because this metal oxidizes rapidly when heated to its melting point in air. all carbon-arc welding should be done in the flat welding position or on a moderate slope. It can be alloyed with small quantities of other metals. Magnesium. very lightweight. This oil. Magnesium is a white. high strength metal. MAGNESIUM WELDING a. machinable. Weldments subjected to corrosive attack over a period of time may crack adjacent to welds if the residual stresses are not removed. the solidification range increases and the melting point and the thermal expansion decrease as the alloy content increases. 7-20. The welds produced between similar alloys will develop the full strength of the base metals. (5) The absence of color change as temperature approaches the melting point. (4) Relatively low melting temperature. a protective inert gas shield must be provided in arc welding to prevent destructive oxidation. In all magnesium alloys. If possible. (2) High thermal conductivity. Stress relieving is required for weldments intended for this type of service. Zinc of more than 1 percent increases hot shortness. because it is faster and more uniform in its action. b. The normal metallurgical factors that apply to other metals apply to magnesium as well. however. An oil coating or chrome pickle finish is usually provided on magnesium alloys for surface protection during shipment and storage. It can be welded by most of the welding processes used in the metal working trades. zinc and zirconium. manganese. Chemical cleaning is preferred. The high zinc alloys are not recommended for arc welding because of their cracking tendencies. General.

instead. and seek medical attention. trichloroethylene. and air dried. or by wire brushing. Dry cleaning solvent and mineral spirits paint thinner evaporate quickly and have a defatting effect on the skin. Grease may also be removed by dipping small parts in dry cleaning solvent or mineral spirits paint thinner. and perchloroethylene) break down under the ultraviolet radiation of an electric arc and form a toxic gas. When spilled on the body or clothing. and prolonged inhalation of the vapor can be hazardous. Avoid welding where such vapors are present.g. thoroughly rinsed with hot water. the metal should be dipped for 3 minutes in a hot solution with the following composition:
The bath should be operated at 70°F (21°C). The welding rod should also be cleaned to obtain the best results. rubber gloves. The various methods for cleaning magnesium are described below. Do not clean parts near an open flame or in a smoking area. These solvents vaporize easily. (3) Immediately after the grease..recommended for parts that are to be arc welded. (1) Grease should be removed by the vapor degreasing system in which trichloroethylene is utilized or with a hot alkaline cleaning compound. and rubber aprons should be worn when handling the acids and solutions.
. Cleaning operations should be performed only in well ventilated areas. oil. Cleaning operations should be performed only in well ventilated areas. These organic vapors should be removed from the work area before welding begins. When used without protective gloves. Do not inhale fumes and mists. WARNING The vapors from some chlorinated solvents (e. carbon tetrachloride. pour acid into water. stainless steel wool. these chemicals may cause irritation or cracking of the skin. Always mix acid and water slowly. Dry cleaning solvent and mineral spirits paint thinner are highly flammable. Goggles. and other foreign materials have been removed from the surface. (2) Mechanical cleaning can be done satisfactorily with 160 and 240 grit aluminum oxide abrasive cloth. WARNING Precleaning and postcleaning acids used in magnesium welding and brazing are highly toxic and corrosive. Never pour water into acid when preparing solution. wash immediately with large quantities of cold water. The work should be removed from the solution.

Joint preparations for arc welding various gauges of magnesium are shown in figure 7-13. Joint Preparation. such as oil or oxides.e.
. Edges that are to be welded must be smooth and free of loose pieces and cavities that might contain contaminating agents.

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(4) The two magnesium alloys. (6.8 mm) thick. in the form of sheet. However. shavings. The preferred extinguishing agents for magnesium fires are graphite base powders. Magnesium scrap of this type is not common to welding operations. it can be extinguished with dry sand. alternating current machines are used on material over 3/16 in. Safety Precautions. with sound welds of high strength. which is alloyed with aluminum. Finely divided magnesium particles such as grinding dust. and extrusion. which is alloyed with manganese. (3) The tungsten electrodes are held in a water cooled torch equipped with required electrical cables and an inlet and nozzle for the inert gas.f. less preparation is required for welding with alternating current than welding with direct current because of the greater penetration obtained. that are most commonly used for applications involving welding are ASTM-1A (Fed Spec QQ-M-54). (1) Goggles. If a magnesium fire does start. The temperature of initial fusion must be reached before solid magnesium metal ignites. or dry cast iron chips. and chips present a fire hazard. filings. Sheets over 1/4 in.4 mm) thickness may be welded from one side with a square butt joint. and zinc. Sheets up to 1/4 in. For a double V
. (5) In general. g. manganese. (2) Direct current machines of the constant current type operating on straight polarity (electrode positive) and alternating current machines are used with a high frequency current superimposed on the welding current. an inert gas (argon or helium) is used to shield metal during arc welding. plate. dry powdered soapstone. CAUTION Magnesium can ignite and burn when heated in the open atmosphere.4 mm) thickness should be welded from both sides whenever the nature of the structure permits. because of better penetrating power. three times as much helium by volume as argon is required for a given amount of welding. (2) The possibility of fire caused by welding magnesium metal is very remote. Argon is used with alternating current. (1) Because of its rapid oxidation when magnesium is heated to its melting point. Gas Tungsten-Arc (TIG) Welding (GTAW) of Magnesium. as sounder welds may be obtained with less warpages. Helium is considered more practical than argon for use with direct current reverse polarity. They ignite readily if proper precautions are not taken. and ASTM-AZ31A (Fed SPec QQ-44). borings. gloves. Both alternating and direct current machines are used for thin gauge material. However. (4. and other equipment designed to protect the eyes and skin of the welder must be worn. This process requires no flux and permits high welding speeds. Sustained burning occurs only if this temperature is maintained. (6.

The average arc length should be about 1/8 in. maximum penetration is obtained when the end of the electrode is held flush with or slightly below the surface of the work. and the welding rod added from a position as neatly parallel with the work as possible (fig. (6) The gas should start flowing a fraction of a second before the arc is struck. With alternating current. dirt.
. The arc is struck by brushing the electrode over the surface.
(7) When welding with alternating current. 7-14). The torch should be held nearly perpendicular to the surface of the work. In this manner. the included angle should extend from both sides to leave a minimum 1/16 in. Current data and rod diameter are shown in table 7-24. (3.joint. When welding a double V joint. The torch should have a slightly leading travel angle. Remove oxide film.2 mm) when using helium and 1/16 in. the arc should be started and stopped by means of a remote control switch. maximum soundness is obtained. and incompletely fused areas before the second bead is added.6 mm) root face in the center of the sheets. (1. the back of the first bead should be chipped out using a chipping hammer fitted with a cape chisel. (1.6 mm) when using argon.

figure 7-15. The cold wire filler metal should be brought in as near to horizontal as possible (on flat work). The welding rod can be fed either continuously or intermittently. starting and stopping plates may be used to overcome this difficult. and a properly selected welding sequence to help minimize distortion. There should be no rotary or weaving motion of the rod or torch. (10) If cracking is encountered during the welding of certain magnesium alloys. The weld is started on one of the abutting plates.
. Forehand welding. except for larger corner joints or fillet welds.(8) Welding should progress in a straight line at a uniform speed. If a V groove is used. The filler wire is added to the leading edge of the weld puddle. and stopped on the opposite abutting plate. continued across the junction along the joint to be welded. fig. the abutting plates should also be grooved.7 mm) back from the end of the weld when welding is resumed. Runoff tabs are recommended for welding any except the thinner metals. These plates consist of scrap pieces of magnesium stock butted against opposite ends of the joint to be welded as shown in A. 7-15). Cracking may also be minimized by preheating the plate and holding the jig to 200 to 400°F (93 to 204°C) by increasing the speed of the weld. (9) Because of the high coefficient of thermal expansion and conductivity. is preferred. Care should be taken to avoid withdrawing the heated end from the protective gaseous atmosphere during the welding operation. care must be taken not to overheat the metal and destroy its properties. control of distortion in the welding of magnesium requires jigging. If this heating is done by local torch application. the weld should be started about 1/2 in. in which the welding rod precedes the torch in the direction of welding. small beads. If stops are necessary. An alternate method is to start the weld in the middle of the joint and weld to each edge (B. (12. Magnesium parts can be straightened by holding them in position with clamps and heating to 300 to 400°F (149 to 204°C).

which produces a stronger weld metal.8 1). Brushing may leave traces of iron. One exception is when welding AZ31B. 16 oz (453 g) sodium metaborate (NaBO2). If necessary.
(13) The only cleaning required after arc welding of magnesium alloys is wire brushing to remove the slight oxide deposit on the surface. Arc welding smoke can be removed by immersing the parts for 1/2 to 2 minutes at 180 to 212°F (82 to 100°C). which may cause galvanic corrosion.(11) Filler reds must be of the same composition as the alloy being joined when arc welding. is used to reduce cracking. in a solution composed of 16 oz (453 g) tetrasodium pyrophosphate (Na4P2O7). clean as in b above. (14) Welding procedure schedules for GTAW of magnesium (TIG welding) are shown in table 7-26. and enough water to make 1 gallon (3. In this case.
. grade C rod (MIL-R6944). The recommended stress relieving treatment for arc welding magnesium sheet is shown in table 7-25. (12) Residual stress should be relieved through heat treatment. Stress relief is essential so that lockup stresses will not cause stress corrosion cracking.

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The normal wire feeder and power supply used for aluminum welding is suitable for welding magnesium.h. argon-helium mixtures can be used. Different types of arc transfer can be obtained when welding magnesium. the spray transfer should be used on material 3/16 in. Welding procedure schedules for GMAW of magnesium (MIG welding) are shown in table 7-27. The short-circuiting transfer and the spray transfer are recommended. however. It is considerably faster than gas tungsten arc welding. In general.
.8 mm) and thicker and the short-circuiting arc used for thinner metals. The gas metal arc welding process is used for the medium to thicker sections. Special high-speed gear ratios are usually required in the wire feeders since the magnesium electrode wire has an extremely high meltoff rate. This is primarily a matter of current level or current density and voltage setting. Gas Metal-Arc (MIG) Welding of Magnesium (GMAW). Argon is usually used for gas metal arc welding of magnesium. (4.

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(5) The procedures for welding titanium and titanium alloys are similar to other metals. (1) Titanium is a soft. Magnesium can be welded using the resistance welding processes. and its tensile strength increases as the temperature decreases. titanium has an impervious oxide coating that resists further reaction with air. including spot welding. silvery white. and plasma-arc welded. 7-21. Other Welding Processes. cannot be welded with any process that utilizes fluxes. cannot be used due to the high chemical activity of titanium and its sensitivity to embrittlement by contamination. and pressure welding. medium strength metal with very good corrosion resistance. such as oxyacetylene or arc welding processes using active gases. In all cases. gas welded. The oxidized coating may enter molten weld metal and create discontinuities which greatly reduce the strength and ductility of the weld. since the strength of the joint is relatively low. Processes that are satisfactory for welding titanium and titanium alloys include gas shielded metal-arc welding. Magnesium can also be joined by brazing. The recrystallization of the metal during welding can raise the transition temperature. seam. gas tungsten arc welding. (2) Titanium has a high affinity for oxygen and other gases at elevated temperatures. This refers to a temperature at which the metal breaks in a brittle manner. It has seizing tendencies at temperatures above 800°F (427°C). and flash welding. The oxide coating melts at temperatures considerably higher than the melting point of the base metal and creates problems. and spot. brazing flux is required and the flux residue must be completely removed from the finish part. rather than in a ductile fashion. flash. It has a high strength to weight ratio. Backing bars that provide inert gas to shield the back of the welds from air are also used. TITANIUM WELDING a. it will make the welding worthless. (4) At room temperature. Some processes. or where heated metal is exposed to the atmosphere. (3) Titanium has the characteristic known as the ductile-brittle transition. Minor amounts of impurities cause titanium to become brittle. Most of the different brazing techniques can be used. Soldering is not as effective. These temperatures range from 700°F (371°C) up to 1000°F (538°C). Gas contamination can occur at temperatures below the melting point of the metal. Titanium has low impact and creep strengths. and for this reason. General. Contamination during the high temperate period and impurities can raise the transition temperature period and impurities can raise the transition temperature so that the material is brittle at room temperatures. seam welding. Special procedures must be employed when using the gas shielded welding processes. Not only the
. If contamination occurs so that transition temperature is raised sufficiently. These special procedures include the use of large gas nozzles and trailing shields to shield the face of the weld from air.i. Magnesium can also be stud welded.

Metals to be welded should be pickled for 1 to 20
. rubber gloves. pickling solutions for this operation should have a nitric acid concentration greater than 20 percent. Proper surface cleaning prior to welding reduces contamination of the weld due to surface scale or other foreign materials. Never pour water into acid when preparing the solution. Goggles. and seek medical help. but the material heated above 1000°F (538°C) by the weld must be adequately shielded in order to prevent embrittlement. (2) Several cleaning procedures are used. Surface Preparation. Perform cleaning operations only in well ventilated places. WARNING The nitric acid used to preclean titanium for inert gas shielded arc welding is highly toxic and corrosive. The caustic chemicals (including sodium hydride) used to preclean titanium for inert gas shielded arc welding are highly toxic and corrosive. as this will cause the formation of highly explosive hydrogen gas. depending on the surface condition of the base and filler metals. When spilled on the body or clothing.molten weld metal. Always mix acid and water slowly. rubber gloves. In order to minimize hydrogen pickup. pour acid into water. Prior to welding. Surface conditions most often encountered are as follows: (a) Scale free (as received from the mill). (c) Heavy scale (after hot forming. wash immediately with large quantities of cold water and seek medical help. Goggles. annealing. b. (1) Surface cleaning is important in preparing titanium and its alloys for welding. wash immediately with large quantities of cold water. less than 1300°F (704°C). Do not inhale gases or mists. and rubber aprons must be worn when handling acid and acid solutions. or forging at high temperature). and rubber aprons must be worn when handling these chemicals. instead. titanium and its alloys must be free of all scale and other material that might cause weld contamination. Special care should be taken at all times to prevent any water from coming in contact with the molten bath or any other large amount of sodium hydride. Small amounts of contamination can render titanium completely brittle.. Do not inhale gases and mists. ie. (4) Metals with light oxide scale should be cleaned by acid pickling. (3) Metals that are scale free can be cleaned by simple decreasing. All of these processes provide for shielding of the molten weld metal and heat affected zones. (b) Light scale (after hot forming or annealing at intermediate temperature. When spilled on the body or clothing.

or vaporblasting. (1) General. When welding pure titanium.
. (6) Surfaces of metals that have undergone oxyacetylene flame cutting operations have a very heavy scale. electrode negative (straight polarity). a thoriated tungsten electrode should be used. Selection of the filler metal will depend upon the titanium alloys being joined. Sand. inert gas filler welding chambers (see (3)) are used to provide the required shielding. the next lowest strength alloy should be used as a filler wire. They are satisfactory for manual and automatic installations. The electrode should be ground to a point. The best cleaning method for flame cut surfaces is to remove the contaminated layer and any cracks by machining operations. The electrode may extend 1-1/2 times its diameter beyond the end of the nozzle. contamination of the molten weld metals and adjacent heated zones is minimized by shielding the arc and the root of the weld with inert gases (see (2)(b)) or special backing bars (see (2)(c)). molten sodium hydride salt baths. and may contain microscopic cracks due to excessive contamination of the metallurgical characteristics of the alloys. Both the MIG and TIG welding processes are used to weld titanium and titanium alloys.minutes at a bath temperature from 80 to 160°F (27 to 71°C). the weld deposit will pick up the required strength. This stress relief is usually made in conjunction with the cutting operation. grit. Bath temperature should be held at about 750 to 850°F (399 to 454°C). When welding a titanium alloy. MIG or TIG Welding of titanium. Due to the dilution which will take place dining welding. The electrode size should be the smallest diameter that will carry the welding current. After pickling. Hydrogen pickup may occur with molten bath treatments. or vaporblasting is preferred where applicable. Welding procedure for TIG welding titanium are shown in table 7-28. a pure titanium wire should be used. Welding is done with direct current. When using the TIG welding process. or molten caustic baths. the parts are rinsed in hot water. grit. c. After heavy scale is removed. Parts should not be pickled any longer than necessary to remove scale. (5) Metals with a heavy scale should be cleaned with sand. The same considerations are true when MIG welding titanium. In some cases. Certain alloys can be stress relieved immediately after cutting to prevent the propagation of these cracks. but it can be minimized by controlling the bath temperature and pickling time. the metal should be pickled as described in (4) above. With these processes.

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Both helium and argon are used as the shielding gases. With mixtures. however. rigid. For thicker metal. Very good shielding conditions are necessary to produce arc welded joints with maximum ductility and toughness. Chill bars often are used to limit the size of the puddle. Backup gas shielding should be provided to protect the underside of the weld joint. This shielding is provided by special trailing gas nozzles. The most critical area in regard to the shielding is the molten weld puddle. If the contact is close enough. adjacent heated zones must be very low. For critical applications. and the thickness of the materials being joined. These can be flexible. To provide adequate shielding for the face and root sides of welds. The bead should be shiny. Impurities diffuse into the molten metal very rapidly and remain in solution. (b) Inert gases. Any discoloration of the surface indicates a contamination. backup shielding gas is not required. The precautions include the use of screens and baffles (see (c) 3). The mixtures usually vary in composition from about 20 to 80 percent argon. Protection of the back side of the joint can also be provided by placing chill bars in intimate contact with the backing strips. special precautions often are taken. welding conditions. the molten puddle tends to be larger than most metals. larger nozzles are used on the welding torch. but the arc is more stable in argon. They are often used with the consumable electrode process. the arc characteristics of both helium and argon are obtained. 1. most welders prefer argon as the shielding gas because its density is greater than that of air. Extra gas shielding provides protection for the heated solid metal next to the weld metal. the methods used to shield the face of the weld vary with joint design. or vacuum-purge chambers.
. With helium as the shielding gas high welding speeds and better penetration are obtained than with argon. and special backing fixtures (see (c) 10) in open air welding. use an inert gas welding chamber. (c) Open air welding. the amount of air or other active gases which contact the molten weld metals and. For open air welding operations. and the use of inert gas filler welding chambers. To obtain these conditions. The gas flowing through a standard welding torch is sufficient to shield the molten zone. with proportionally higher gas flows that are required for other metals. (a) General. Welding grade shielding gases are generally free from contamination. trailing shields (see (c) 7). use helium or a mixture of argon and helium. and notice its color. In open air welding operations. For this reason and because of shielding conditions required in welding titanium. however. or by chill bars laid immediately next to the weld. Mixtures of argon and helium are also used. tests can be made before welding. A simple test is to make a bead on a piece of clean scrap titanium. Because of the low thermal conductivity of titanium.(2) Shielding. Argon is normally used with the gasshielded process.

The impurities go into solution. and joint design. Baffles protect the weld from drafts and tend to retard the flow of shielding gas from the joint area. Even with proper manipulation. insufficient gas flow. the hot end of the filler wire must be kept within the gas shield of the welding torch. and impure shielding gases. The latter three sources are easily controlled. Contamination from this source can be minimized by adjusting gas flows and arc lengths. however. and do not cause discoloration. air will be inspired and contamination will result. 5. and by placing baffles alongside the welds. The primary sources of contamination in the molten weld puddle are turbulence in the gas flow. To control it. Welding operators must be trained to keep the filler wire shielded when welding titanium and its alloys. Although discolored welds may have been improperly shielded while molten. 3. small nozzles on the welding torch. 6. oxidation of hot filler reds. Weld contamination which occurs in the molten weld puddle is especially hazardous. Additional precautions can be taken to protect the operation from drafts and turbulence. In manual welding operations with the tungsten-arc process. If turbulence occurs in the gas flowing from the torch. long arc lengths. Most of the auxiliary equipment used on torches to weld titanium is designed to improve shielding conditions for the welds as they solidify
. Chill bars or the clamping toes of the welding jig can serve as baffles (fig. weld discoloration is usually caused by contamination which occurs after the weld has solidified. contamination from this source probably cannot be eliminated completely. This can be achieved by erecting a canvas (or other suitable material) screen around the work area. 716). oxidation of the hot filler metal is a very important source of contamination. Turbulence is generally caused by excessive amounts of gas flowing through the torch.2. Baffles are especially important for making corner type welds. air currents blowing across the weld.
4.

However. or at the ends of the weld. auxiliary shielding must be supplied. Also. Backing fixtures are often used for this purpose.and cool. Trailing shields often are used to supply auxiliary shielding. This will prevent turbulence in the gas stream. If the weld is at an excessively high temperature after it is no longer shielded by the welding torch. However. These shields extend behind the welding torch and vary considerably in size. means must be provided for shielding the root or back of the welds. The shield fits on the torch so that a continuous gas stream between the torch and shield is obtained.
8. shaper and design. they may actually form a chamber around the arc and molten weld puddle. or may consist only of tubes or hoses attached to the torch or manipulated by hand to direct a stream of inert gas on the welds. 7. chill bars may be used to increase weld cooling rates and may make auxiliary shielding unnecessary. They are incorporated into special cups which are used on the welding torch. over the top. 10. In open air welding operations. an auxiliary supply of inert gas is provided to shield the back of the weld. In the other. a solid or grooved backing bar fits
. 9. Very little difficulty has been encountered in shielding the face of welds in automatic welding operations. Important features of this shield are that the porous diffusion plate allows an even flow of gas over the shielded area. if the welding heat input is low and the weld cools to temperatures below about 1200 to 1300°F (649 to 704°C) while shielded. In one type. Baffles may be placed alongside the weld. Figure 7-17 shows a drawing of one type of trailing shield currently in use. auxiliary shielding equipment is not required. considerable difficulty has been encountered in manual operations. Baffles are also beneficial in improving shielding conditions for welds by retarding the flow of shielding gas from the joint area. In some instances.

WARNING When using weld backup tape. or other enclosed structures where access to the back of the weld is not possible. the weld must be allowed to cool for several minutes before attempting to remove the tape from the workpiece. 12. This method is necessary in welding tanks. Fixtures which provide an inert gas shield are preferred. as in a tank. respectively. For fillet welds on tee joints. the design of the fixtures varies with the design of the joints. Figure 7-18 shows backing fixtures used in butt welding heavy plate and thin sheet. For some applications. it may be easier to enclose the back of the weld. it may be necessary to machine holes or grooves in the structures in order to provide shielding gas for the back or root of the welds. In some weldments. This tape consists of a center strip of heat resistant fiberglass adhered to a wider strip of
. Use of backing fixtures such as shown in figure 7-18 can be eliminated in many cases by the use of weld backup tape.tightly against the back of the weld and provides the required shielding. However.
11. shielding should be supplied for two sides of the weld in addition to shielding the face of the weld. especially in manual welding operations with low welding speeds. and supply inert gas for shielding purposes. Similar types of fixtures are used for other joint designs. tubes.

the weld surface may be shiny but have different colors. Best results are obtained by using a root gap wide enough to allow full penetration. the quality of the weld cannot be determined without a destructive test. which is not an infallible method. the presence of a heavy gray scale with a nonmetallic luster on the weld bead indicates that the weld has been contaminate badly and has low ductility. preventing excessive penetration. while the weld itself may be satisfactory. on curved or irregularly shaped surfaces. is the only nondestructive means for evaluating weld quality at the present time. but visual inspection of the weld surface. ranging from grayish blue to violet to brown. because of its flexibility.
.
13. The surface to which the tape is applied must be clean and dry. This type of discoloration may be found on severely contaminated welds or may be due only to surface contamination. weld surfaces are shiny and show no discoloration. along with a strip of adhesive on each side of the center strip that is used to hold tape to the underside of the tack welded joint.aluminum foil. Contamination or oxidation of the underside of the weld is prevented by the airtight seal created by the aluminum foil strip. During the welding. With this method. 7-19) or. Bend or notch toughness tests are the best methods for evaluating shielding conditions. the fiberglass portion of the tape is in direct contact with the molten metal. With good shielding procedures. However. Also. The tape can be used on butt or corner joints (fig.

bars. the width of the beads is generally controlled by using short arc lengths. penetration and dropthrough are controlled more easily by the use of proper backing fixtures. depending on their use and the size of assemblies to be welded. design of the backing fixtures. In all cases. or forgings.2 to 1016. The use of chambers is especially advantageous when complex joints are being welded. (4) Joint designs. The inert atmospheres maybe obtained by evacuating the chamber and filling it with helium or argon. and their use may be limited. Also. The advantage of using such chambers is that good shielding may be obtained for the root and face of the weld without the use of special fixtures. chambers are not required for many applications.0 to 40. Joint designs for titanium are similar to those used for other metals. purging the chamber with inert gas. shielding gas. along with the spacing of chill bars or clamping bars in the welding jig. the tungsten-arc process generally is used. When the atmospheres are obtained by purging or collapsing the chambers. or collapsing the chamber to expel air and refilling it with an inert gas.
. Welding speeds vary from about 3. direct current is used with straight polarity for the tungsten-arc process. or by placing chill bars or the clamping toes of the jig close to the sides of the joints. thickness of the material being welded. inert gas usually is supplied through the welding torch to insure complete protection of the welds. butt welds may be made with or without filler rod. Special shearing procedures sometimes are used so that the root opening does not exceed 8 percent of the sheet thickness. good weld penetration may be obtained with excessive drop through. For welding titanium plates. If fitup is this good. (2. For welding a thin sheet. filler rod is not required.0 mm) per minute. The highest welding speeds are obtained with the consumable electrode process. If fitup is not this good. However. both the tungsten-arc and consumable electrode processes also are used with single and double V joints. depending on the thickness of the joint and fitup.0 in. However.(3) Welding chambers.09 in. (a) Welding speed and current for titanium alloys depend on the process used. (b) Welding chambers vary in size and shape. the surface appearance of such welds is a fairly reliable measure of shielding conditions.3 mm)). NOTE Because of the low thermal conductivity of titanium. (5) Welding variables. weld beads tend to be wider than normal. (76. Plastic bags have been used in this latter manner. Reverse polarity is used for the consumable electrode process. (a) For some applications. In most cases. inert gas filled welding chambers are used. filler metal is added to obtain full thickness joints. In welding thicker sheets (greater than 0. However. both the tungsten-arc and consumable electrode processes are used with a root opening. With this process.

1. These machines also have not been completely satisfactory. A straight. porosity has been observed in tungsten-arc welds in practically all of the alloys which appear suitable for welding operations. remelting the weld will eliminate some of the porosity present after the first pass. Weld penetration can be controlled by adjusting welding conditions. Also. Arc wander is believed to be caused by magnetic disturbances.(b) Arc wander has proven troublesome in some automatic welding operations. cracks in these alloys also may be due to contamination. weld metal cracks are believed to be caused by excessive oxygen or nitrogen contamination. careful controls are desirable to ensure that the shielding conditions are not changed. the welding conditions should be evaluated on the basis of weld joint properties and appearance. the latter method of reducing weld porosity tends to increase weld contamination. bends in the filler wire. In commercially pure titanium. (c) Cracks. (b) Porosity. Special metal shields and wire straighteners have been used to overcome arc wander. cracks should not be a problem. Radiographs will show if porosity or cracking is present in the weld joint. but has been detected in radiographs. Weld cracks are attributed to a number of causes. Cracks also have been observed in alpha-
. However. constant voltage welding machines have been used in an attempt to overcome this problem. Weld porosity may be reduced by agitating the molten weld puddle and adjusting welding speeds. A simple bend test or notch toughness test will show whether or not the shielding conditions are adequate. but have not been completely satisfactory. It does not extend to the surface of the weld. A visual examination of the weld will show if the weld penetration and contour are satisfactory. cracks have been troublesome in welding some alloys. uniform weld bead will not be produced. (6) Weld defects. (c) In setting up arc welding operations for titanium. (a) General. Although acceptable limits for porosity in arc welded joints have not been establish. It usually occurs close to the fusion line of the welds. or a combination of these. However. With adequate shielding procedures and suitable alloys. With arc wander. coatings on the filler wire. the arc from the tungsten or consumable electrode moves from one side of the weld joint to the other side. After adequate procedures are established. Also. Defects in arc welded joints in titanium alloys consist mainly of porosity (see (b)) and cold cracks (see (c)). These cracks are usually observed in weld craters. transverse cracks in the weld metal and heat affected zones are believed to be due to the low ductility of the weld zones. Weld porosity is a major problem in arc welding titanium alloys. However. In some of the alpha-beta alloys.

Pressure Welding. They are held together under pressure and heated to elevated temperatures (900 to 2000°F (482 to 1093°C)). These alloys are listed below: (a) Commercially pure titanium --commercially available as wire. it may be controlled by improving shielding conditions. With all of the heating methods. However. However. However. Cracks due to hydrogen may be prevented by vacuum annealing treatments prior to welding. (e) There has not been a great deal of need for the other alloys as welding filler wires. In fact. most of these alloys also could be reduced to wire. One method of heating used in pressure welding is the oxyacetylene flame. Cracks which are caused by the low ductility of welds in alpha-beta alloys can be prevented by heat treating or stress relieving the weldment in a furnance immediately after welding. repair welding on excessively contaminated welds is not practical in many cases. (b) Ti-5A1-2-1/2Sn alloy --available as wire in experimental quantities. By heating in this manner. NOTE If weld cracking is due to contamination. (7) Availability of welding filler wire. 3. Oxyacetylene torches also have been used for this purpose. care must be taken so that the weldment is not overheated or excessively contaminated by the torch heating operation. The contaminated area on the surface of the weld is displaced from the joint area by the upset. the Ti-8Mn alloy has been furnished as welding wire to meet some requests. d. (d) Ti-6A1-4V alloy --available as wire in experimental quantities. These cracks are sometimes attributed to the hydrogen content of the alloys. Most of the titanium alloys which are being used in arc welding applications are available as wire for use as welding filler metal. In these processes. With solid phase or
. less than 2 minutes is required to complete the welding operation. Solid phase or pressure welding has been used to join titanium and titanium alloys. (c) Ti-1-1/2A1-3Mn alloy --available as wire in experimental quantities. if such a need occurs. 2. which occurs during welding. welds may be made in very short periods of time. Strong lap joints are obtained with this method in commercially pure titanium and a high strength alpha-beta alloy. This contaminated surface is machined off after welding. Another method of heating is by heated dies. With suitable pressure and upset. the surfaces to be jointed are not melted. good welds are obtainable in the high strength alpha-beta titanium alloys.beta welds made under restraint and with high external stresses. and inert gas shielding may be supplied to the joint.

However. be welded by metal-arc and gas welding methods. When compensation is made for these three factors. or impurity. Nickel and nickel alloys such as Monel can. It is necessary to increase the opening of groove angles and to provide adequate root openings when full-penetration welds are used. This is because the melting point. Generally. The operator should make trial welds with reverse polarity at several current values and select the one best suited for the work. Some nickel alloys are more difficult to weld due to different compositions. Nickel and its alloys are commonly used when corrosion resistance is required. It is necessary that each of these precautions be considered. ductile metal. grease. They must be completely removed for the weld area to avoid embrittlement.pressure welding processes. and some low-temperature metals and alloys. the oxyacetylene welding methods are preferred for smaller plates. phosphorus. and large plates are most satisfactorily joined.2 mm) thick. machining. or by chemical means. Joint Design. (2) The nickel alloys are susceptible to embrittlement at welding temperatures by lead. General. b.6 to 3. the nickel alloys can be treated much in the same manner as austenitic stainless steels with a few exceptions. The surface oxide should be completely removed from the joint area by grinding. abrasive blasting. they must be completely removed by rinsing prior to welding. crayon markings. (1. (3) Weld penetration is less than expected with other metals. especially if the plate is nickel clad steel. Beveling is not required on plates 1/16 to 1/8 in. NICKEL AND MONTEL WELDING a. and the thermal conductivity are similar to austenitic stainless steel. and cutting oils may all contain the ingredients which will cause embrittlement. in general. the welding procedures used for the nickel alloys can he the same as those used for stainless steel. small plates can be welded by the metal-arc and carbon-arc processes. The problem of embrittlement at welding temperatures also means that the weld surface must be absolutely clean. When welding. sulfur. These exceptions are: (1) The nickel alloys will acquire a surface or coating which melts at a temperature approximately 1000°F (538°C) above the melting point of the base metal. Butt joints are preferred but corner and lap joints can be effectively welded. oil. it is possible to produce ductile welds in the high strength alpha-beta alloys by using temperatures which do not cause embrittlement in these alloys. and will greatly reduce the strength and ductility of the weld. 7-22. When chemical etches are used. The bevel or groove angles should be increased to approximately 40 percent over those used for carbon steel. malleable. machining lubricants. a
. With thicker materials. Paints. the coefficient of thermal expansion. Nickel is a hard. The oxide which melts at temperatures above the melting point of the base metal may enter the weld as a foreign material.

Welding Methods. the weld should be made entirely with nickel electrodes if water or air tightness is required. and if nickel clad steel. (2) Welding nickel alloys. or chemically by pickling. If the base metal on both sides is nickel. A 1/16 to 1/8 in. In addition. Chip out and clean the nickel side and weld.bevel angle of 35 to 37-1/2 degrees should be made. However. When shielded metal arc welding is used the procedures are essentially the same as those used for stainless steel welding. the gas tungsten arc welding process. the steel side must be tacked and thoroughly cleaned and beveled (or gouged) down to the root of the nickel weld prior to welding. grinding. (5) The arc drawn for nickel or nickel alloy welding should be slightly shorter than that used in normal metal-arc welding. the nickel side may be completed first. (4) Lap and corner joints are successfully welded by depositing a bead of nickel metal into the root and then weaving successive beads over the root weld.6 to 3. When welding lap joints. or with abrasive cloth. complete the weld on the steel side.2 mm) arc is a necessity. The procedure information set forth on these tables will provide starting points for developing the welding procedures. The most popular processes for welding nickel alloys are the shielded metal arc welding process. The welding procedure schedule for using gas tungsten arc welding (TIG) is shown by table 7-29. Process selection depends on the normal factors. (6) Any position weld can be accomplished that can be satisfactorily welded by normal metal-arc welding of steel. should be tacked on the steel side to prevent warping and distortion. (1. they can be joined by brazing and soldering.
. d. (1) Clean all surfaces to be welded either mechanically by machine. After it is determined that the joint is even and flat. (1) Almost all the welding processes can be used for welding the nickel alloys. The welding procedure schedule for gas metal arc welding (MIG) is shown by table 7-30. clean out the groove on the unwelded side prior to beginning the weld on that side. and the gas metal arc welding process. (3) If desired. Welding Techniques. sand-blasting. (2) Plates having U or V joints should be assembled. c.

tough coating. The metal-arc electrodes may be grouped and classified as bare or thinly coated electrodes. as well as the composition of the deposited weld metal and the electrode specification. The coatings of electrodes for welding mild and low alloy steels may have from 6 to 12 ingredients. When molten metal is exposed to air. The type of electrode used depends on the specific properties required in the weld deposited. This cover can be obtained from the electrode coating. which include: (1) Smooth weld metal surface with even edges. it absorbs oxygen and nitrogen. COVERED ELECTRODES a. The formulation of electrode coatings is based on well-established principles of metallurgy. and the type of current and polarity required. chemistry. Types of Electrodes. The covered electrode is the most popular type of filler metal used in arc welding. (4) Penetration control. and improves the weld in other ways. TYPES OF ELECTRODES
8-1. The composition of the electrode covering determines the usability of the electrode. which include cellulose to provide a gaseous shield with a reducing agent in which the gas shield surrounding the arc is produced by the disintegration of cellulose. (2) Minimum spatter adjacent to the weld. and physics. the composition of the deposited weld metal. and the specification of the electrode. General. or overhead). and becomes brittle or is otherwise adversely affected. horizontal. The coating protects the metal from damage. (6) Easier slag removal. b. (5) A strong. The composition of the electrode coating determines its usability.CHAPTER 8 ELECTRODES AND FILLER METALS
Section I. the type of base metal to be welded. These include corrosion resistance. metal carbonates to adjust the basicity of the slag and to provide a reducing
. (7) Improved deposition rate. high tensile strength. (3) A stable welding arc. vertical. ductility. and shielded arc or heavy coated electrodes. A slag cover is needed to protect molten or solidifying weld metal from the atmosphere. the position of the weld (flat. stabilizes the arc.

calcium fluoride to provide shielding gas to protect the arc. This electrode coating is very similar to the rutile-sodium type. These gases tend to produce a digging arc that provides deep penetration. (2) Cellulose-potassium (EXX11). which are reducing agents. It does provide extremely good mechanical properties. iron or manganese oxide to adjust the fluidity and properties of the slag and to help stabilize the arc. and iron powder to increase the productivity by providing extra metal to be deposited in the weld. except that iron powder is added.atmosphere. mineral silicates to provide slag and give strength to the electrode covering. This assists in arc stabilization and will slightly increase the deposition rate. Electrodes with this coating have a quiet arc. (5) Rutile-iron powder (EXXX4). It is normally used with direct current with the electrode positive (reverse polarity). (1) Cellulose-sodium (EXX10). When rutile or titanium dioxide content is relatively high with respect to the other components. The weld deposit will have a smooth surface and the penetration will be less than with the cellulose electrode. the
. clays and gums to provide elasticity for extruding the plastic coating material and to help provide strength to the coating. This provides ionization of the arc and makes the electrode suitable for welding with alternating current. particularly after aging. except more potassium is used than sodium. It can also be used with direct current with either polarity. This type of electrode provides a fairly high rate of deposition. This electrode is very similar to the cellulose-sodium electrode. except that potassium is used to provide for arc ionization. The principal types of electrode coatings for mild steel and are described below. The gas shield contains carbon dioxide and hydrogen. the penetration. This coating is very similar to the rutile coatings mentioned above. The weld deposit is somewhat rough. This is one of the earliest types of electrodes developed. but quick-freezing slag and to provide ionization for the arc. It has a relatively low arc voltage. and can be used with alternating current or with direct current with electrode negative (straight polarity). It produces a very quiet. (3) Rutile-sodium (EXX12). molybdenum. If iron content is 25 to 40 percent. Electrodes of this type cellulosic material in the form of wood flour or reprocessed low alloy electrodes have up to 30 percent paper. This makes it more suitable for welding with alternating current. an easily controlled slag. alloying metals including nickel. the electrode will be especially appealing to the welder. and is widely used for cross country pipe lines using the downhill welding technique. smooth running arc. and a low level of spatter. In both E6010 and E6011 electrodes. and provide fluidity and solubility of the metal oxides. adjust the basicity of the slag. titanium dioxide to help form a highly fluid. ferromanganese and ferrosilicon to help deoxidize the molten weld metal and to supplement the manganese content and silicon content of the deposited weld metal. and the spatter is at a higher level than other electrodes. The weld metal properties will be slightly lower than the cellulosic types. and the weld results are very similar. The arc action. (4) Rutile-potassium (EXX13). small amounts of iron powder may be added. and chromium to provide alloy content to the deposited weld metal.

This electrode is used with alternating current and can be used with direct current. (8) Low hydrogen-potassium (EXXX6). but has 50 percent or more iron powder in the coating. These electrode coatings are baked at a higher temperature. electrode positive (reverse polarity). These electrodes have a medium arc with medium or moderate penetration. It is usable only when welding in the flat position or for making horizontal fillet welds. based on the amount of iron powder in the coating. it can only be used in the flat position or for making horizontal fillet welds. (7) Low hydrogen-potassium (EXXX6). The deposition rate is higher than EXX18. The electrode can be used with alternating current or direct current with either polarity. except it contains 50 percent or more iron power. However. In this class of coating. This type of coating is similar to the low hydrogen-sodium. This can be difficult to control. and provides medium penetration with low spatter level. This type is normally used with direct current with electrode positive (reverse polarity). (9) Low hydrogen-iron powder (EXX28). This is to ensure the lowest possible hydrogen content in the arc atmosphere. cellulose. The arc action is smother. the electrode is classified as an EXX18. (11) Iron-oxide-iron power (EXX27). the electrode can be used in all positions. asbestos. and other minerals that contain combined water are not used. By additions of specific metals in the coatings. Electrodes for welding stainless steel are also the low-hydrogen type. the deposition rate is increased. iron powder is added to the electrode. the electrode is EXX24. The increased
. (10) Iron oxide-sodium (EXX20). With the lower percentage of iron powder. They provide the highest ductility of any of the deposits. lime ferritic. This type of electrode is very similar to the iron oxide-sodium type. and if the content is higher than 35 to 40 percent. clays. They have a medium speed of deposition. except for the substitution of potassium for sodium to provide arc ionization. This coating type produces high-speed deposition. The resulting weld has a very smooth finish. Low hydrogen coatings are used for all of the higher-alloy electrodes. Coatings that contain a high proportion of calcium carbonate or calcium fluoride are called low hydrogen. but require special welding techniques for best results. The electrode is usable only with flat position welding and for making horizontal fillet welds. these electrodes become the alloy types where suffix letters are used to indicate weld metal compositions. This electrode is similar to the EXX18. If iron content is 50 percent or more. With the higher percentage of iron paler.electrode is EXX14. (6) Low hydrogen-sodium (EXXX5). The coatings in this class of electrodes are similar to the low-hydrogen type mentioned above. Coatings with high iron oxide content produce a weld deposit with a large amount of slag. or basic type electrodes. In both cases. but the penetration of the two electrodes is similar. Low hydrogen electrodes must be stored under controlled conditions. The low hydrogen electrode family has superior weld metal properties.

(12) There are many types of coatings other than those mentioned here. The 50 percent iron power electrode figured on United States standards would produce an efficiency of approximately 150 percent using the European formula. It may be used with alternating direct current of either polarity. and for nonferrous metals. This is based on the amount of iron power in the coating versus the coating weight. This is shown in the formula:
These percentages are related to the requirements of the American Welding Society (AWS) specifications. They are listed under the E45 series in the electrode identification system. the percentage of iron power in a coating is in the 10 to 50 percent range. A light coating has been applied on the surface by washing. sulfur. The electrodes containing iron power in the coating have the highest deposition rates. and phosphorus. (2) The coating generally serves the functions described below: (a) It dissolves or reduces impurities such as oxides. Light Coated Electrodes. cast iron welding. The 30 percent iron power formula used in the United States would produce a 100 to 110 percent deposition efficiency using the European formula. d.
. most of which are usually combinations of these types but for special applications such as hard surfacing. it would indicate a 200 percent deposition efficiency. Deposition Rates. refer to paragraph 5-25. spraying. This is shown as follows:
Thus. Classification and Storage of Electrodes. In the United States. if the weight of the deposit were double the weight of the core wire. tumbling. The different types of electrodes have different deposition rates due to the composition of the coating. c. (1) Light coated electrodes have a definite composition. Refer to paragraph 5-25 for classification and storage of electrodes. dipping. or wiping. brushing. The coatings improve the characteristics of the arc stream. even though the amount of the iron power in the coating represented only half of the total deposit. The European method of specifying iron power is based on the weight of deposited weld metal versus the weight of the bare core wire consumed.amount of iron power greatly increases the deposition rate. e.

(c) It increases the arc stability by introducing materials readily ionized (i. (4) By reducing the attractive force between the molten metal and the end of the electrodes. sodium. (2) They reduce impurities such as oxides. and other inorganic substances or combinations thereof.
. the vaporized and melted coating causes the molten metal at the end of the electrode to break up into fine. The slag is quite thin and does not act in the same manner as the shielded arc electrode type slag. f. The mineral coated electrode forms a slag deposit. (3) They provide substances to the arc which increase its stability. This helps make flow of molten metal more uniform. cast iron. it holds the heat and allows the underlying metal to cool and solidify slowly. Slow cooling also has an annealing effect on the weld deposit.. or titanium. small particles. metallic oxides clay. The electrodes are manufactured in three general types: those with cellulose coatings. or by reducing the surface tension of the molten metal. Cellulose coated electrodes protect the molten metal with a gaseous zone around the arc as well as the weld zone. (5) The coatings contain silicates which will form a slag over the molten weld and base metal. The shielded arc or heavy coated electrodes are used for welding steels. changed into small particles with an electric charge) into the arc stream. Since the slag solidifies at a relatively slow rate.(b) It changes the surface tension of the molten metal so that the globules of metal leaving the end of the electrode are smaller and more frequent. low ductility. and those whose coatings are combinations of mineral and cellulose. and in Some cases low strength and poor resistance to corrosion. and in some cases added minerals. those with mineral coatings. g. Nitrogen causes brittleness. Functions of Shielded Arc or Heavy Coated Electrodes. This slow solidification of the metal eliminates the entrapment of gases within the weld and permits solid impurities to float to the surface. The mineral coatings consist of sodium silicate. sulfur. This prevents atmospheric oxygen or nitrogen from contaminating the weld metal. removing alloying elements and causing porosity. (3) Some of the light coatings may produce a slag. and phosphorus so that these impurities will not impair the weld deposit. The oxygen readily combines with the molten metal. The cellulose coatings are composed of soluble cotton or other forms of cellulose with small amounts of potassium. and hard surfacing. Shielded Arc or Heavy Coated Electrodes. (1) These electrodes produce a reducing gas shield around the arc. Shielded arc or heavy coated electrodes have a definite composition on which a coating has been applied by dipping or extrusion.e. This eliminates wide fluctuations in the voltage so that the arc can be maintained without excessive spattering.

(1) The manufacturer's recommendations should be followed when a specific type of electrode is being used. and other specific conditions. Good penetration can be obtained from either type with proper welding conditions and arc manipulation.01 percent). the composition and uniformity of the wire is an important factor in the control of arc stability. the arc stability will be affected. Electrode Defects and Their Effect. brittleness. of the direct current electrodes can be used with alternating current. direct current straight polarity is recommended. j. silicon dioxide.04 percent.(6) The physical characteristics of the weld deposit are modified by incorporating alloying materials in the electrode coating. bare and alloy steel electrodes. (1) Coated electrodes which can be used with either direct or alternating current are available. they will impair the weld metal. direct current shielded arc electrodes are designed either for reverse polarity (electrode positive) or for straight polarity (electrode negative). Arc blow causes blowholes. Direct Current Arc Welding Electrodes. and iron sulfate cause the arc to be unstable. (2) Aluminum or aluminum oxide (even when present in quantities not exceeding 0. Recommendations from the manufacturer also include the type of base metal for which given electrodes are suitable. and "cold shortness"
. Alternating current is more desirable while welding in restricted areas or when using the high currents required for thick sections because it reduces arc blow. It permits a uniform rate of welding and electrode consumption ion. i. manganese oxide. (2) In most cases. Phosphorus causes grain growth. Direct current is preferred for many types of covered nonferrous. Iron oxide. because the electrode will be consumed at a lower rate. (1) If certain elements or oxides are present in electrode coatings. corrections for poor fit-ups. Thin or heavy coatings on the electrodes will not completely remove the effects of defective wire. (2) Alternating current is used in atomic hydrogen welding and in those carbon arc processes that require the use of two carbon electrodes. Many. h. In carbon-arc processes where one carbon electrode is used. slag inclusions. The fluxing action of the slag will also produce weld metal of better quality and permit welding at higher speeds. or both. reverse polarity electrodes will provide more penetration than straight polarity electrodes. silicon. but not all. and iron sulfide tend to stabilize the arc. calcium oxide. Alternating Current Arc Welding Electrodes. They are transferred from the electrode to the molten metal with very little loss. and lack of fusion in the weld. In bare electrodes. (3) When phosphorus or sulfur are present in the electrode in excess of 0. In general.

When the wire is cut and straightened. Solid steel electrode wires may not be bare. The copper coating improves the current pickup between contact tip and the electrode. Bare electrodes are used for welding manganese steels and for other purposes where a covered electrode is not required or is undesirable. Several different systems are used to identify the classification of a particular electrode or welding rod. Solid electrode wires are also made of various stainless steels.
. which is a form of filler metal used for welding or brazing and does not conduct the electrical current. SOLID ELECTRODE WIRES a. d.(i. (4) If the heat treatment given the wire core of an electrode is not uniform. c. These defects increase in magnitude as the carbon content of the steel increases. A sketch of the transfer of metal across the arc of a bare electrode is shown in figure 8-1. the electrode will produce welds inferior to those produced with an electrode of the same composition that has been properly heat treated. Many have a very thin copper coating on the wire. and have no coatings other than those required in wire drawing. Bare or solid wire electrodes are made of wire compositions required for specific applications. it is called a welding electrode. and causes "hot shortness" (i.
b. These wire drawing coatings have a slight stabilizing effect on the arc.e. brittle when above red heat). Manganese promotes the formation of sound welds. (1) Prefix R. and other metals. brittle when below red heat) in the weld. it can take other forms.e. however. but are otherwise of no consequence. Indicates a welding rod. breaks up the soundness of the weld metal. it is called a welding rod. magnesium alloys. 8-2. aids drawing. and is defined as a component of the welding circuit through which current is conducted. copper alloys. Sulfur acts as a slag. In all cases a prefix letter is used. nickel alloys. General. aluminum alloys. titanium alloys. If the wire is used in the electrical circuit. A bare electrode is normally a wire. Sulfur is particularly harmful to bare low carbon steel electrodes with a low manganese content.. and helps prevent rusting of the wire when it is exposed to the atmosphere..

e. (5) 1 suffix number indicates a particular analysis and usability factor. Indicates use as either a welding rod or for brazing filler metal. M for medium..(2) Prefix E. (3) Prefix RB. The system for identifying bare carbon steel electrodes and rods for gas shielded arc welding is as follows: (1) ER indicates an electrode or welding rod. L for low. The system for identifying solid bare carbon steel for submerged arc is as follows: (1) The prefix letter E is used to indicate an electrode. Indicates wither an electrode or welding rod. (4) Prefix ER. (3) S indicates solid electrode or rod. e. (2) 70 indicates the required minimum as-welded tensile strength in thousands of pounds per square inch (psi). Table 8-1. Mild Steel Electrode Wire Composition for Submerged Arc Welding
f. and H for high manganese. Submerged Arc Electrodes. Indicates a welding electrode. i. This is followed by a letter which indicates the level of manganese. (4) C indicates composite metal cored or stranded electrode or rod. This is followed by a number which is the average amount of carbon in
.

followed by the chemical symbol of the principal metals in the wire. The particular specification involved should be used for specifying filler metals. "Bare Mild Steel Electrodes and Fluxes for Submerged Arc Welding. followed by a G indicating that the rod is used expressly for gas welding. i. These designate the approximate tensile strength in 1000 psi (6895 kPa). or 65. which is given by the specification. and may create erratic welding operation. Occasionally. There are also extremely large reels weighing many hundreds of
. Too much dirt will clog the liners.points or hundredths of a percent. or contact tips. When these electrodes are used with specific submerged arc fluxes and welded with proper procedures. This can be checked by using a white cleaning tissue and pulling a length of wire through it. A light copper coating is desirable. There are also military specifications such as the MIL-E or -R types and federal specifications. If there is more than one alloy containing the same elements. The most important aspect of solid electrode wires and rods in their composition. on copper-plated solid wires. The minimum tensile strength recommended by the specification is 140. This information is given in table 8-1. the prefix letter is R. h. through medium-size spools for fine-wire gas metal arc welding." This specification provides both the wire composition and the weld deposit chemistry based on the flux used. Wire of a higher strength will feed through guns and cables better. Coils of electrode wire are available which can be placed on reels that are a part of the welding equipment. These letters are followed by two digits which will be 45. (3) In the case of the filler reds used for oxyfuel gas welding. the prefix E. The composition of some of these wires is almost identical with some of the wires in the gas metal arc welding specification. g. The specifications provide the limits of composition for the different wires and mechanical property requirements. the deposited weld metal will meet mechanical properties required by the specification. or RB is used. The continuous electrode wire is available in many different packages. j.300 kPa). normally the QQ-R type and AMS specifications. reduce current pickup in the tip. The electrode wire surface should be reasonably free of dirt and drawing compounds. They range from extremely small spools that are used on spool guns. the copper may flake off in the feed roll mechanism and create problems. The initials for one or two elements will follow. (5) The American Welding Society's specifications are most widely used for specifying bare welding rod and electrode wires.000 psi (965. It may plug liners. The specification does give composition of the electrode wires. Temper or strength of the wire can be checked in a testing machine. (4) In the case of nonferrous filler metals. (2) The electrode wires used for submerged arc welding are given in American Welding Society specification. R. a suffix letter or number may be added. 60.

The compounds contained in the electrode perform essentially the same functions as the coating on a covered electrode. The electrode wire is also available in drums or payoff packs where the wire is laid in the round container and pulled from the container by an automatic wire feeder. b. especially for welding pipe in the fixed position. This inside-outside electrode consists of a metal sheath surrounding a core of fluxing and alloying compounds. arc stabilizers. General. These billets are not readily available and are expensive.e. For a covered electrode. the special alloying elements are introduced in the core material to provide the proper deposit analysis. Solid wires are drawn from steel billets of the specified analyses. In the case of cored wires. and the core material represents 10 to 25 percent of the weight of the electrode. 8-3. This is shown in more detail below: Flux Cored Electrode Wire (E70T-1) Covered Electrode (E7016)
By area
Flux steel
25% 75% 15% 85%
By area
Flux steel
55% 45% 24% 76%
By weight
Flux steel
By weight
Flux steel
. The flux-cored arc welding process is made possible by the design of the electrode. slag formers. The sheath or steel portion of the flux-cored wire comprises 75 to 90 percent of the weight of the electrode. deoxidizers. (2) Tubular wire production method provides versatility of composition and is not limited to the analysis of available steel billets. There are three reasons why cored wires are developed to supplement solid electrode wires of the same or similar analysis. i. the steel represents 75 percent of the weight and the flux 25 percent. FLUX-CORED OR TUBULAR ELECTRODES a.pounds.. A single billet might also provide more solid electrode wire than needed. alloying elements. (3) Tubular electrode wires are easier for the welder to use than solid wires of the same deposit analysis. Flux-Cored Electrode Design. (1) There is an economic advantage. and may provide shielding gas.

000 psi (289. Other codes prohibit the self-shielding wires from being used on dynamically loaded structures. lower the ductility. The properties of the weld metal deposited by the self-shielding wires are sometimes inferior to those produced by the externally shielded electrode wires because of the extra amount of deoxidizers included. Metal Transfer. (1) E60T-7 electrode classification. but is specific for tubular electrodes. The larger droplets at the lower currents cause a certain amount of splashing action when they enter the weld puddle. Transfer is more frequent with smaller drops when the current is increased. These are spray transfer. Self-shielding electrodes also include extra deoxidizing and denigrating elements to compensate for oxygen and nitrogen which may contact the molten metal. On cored electrodes in a carbon dioxide shielding atmosphere. the droplets tend to be larger than when the current density is increased. e. and reduce the impact values of the deposit. These are necessary to prohibit the oxygen and nitrogen of the air from contacting the metal transferring across the arc and the molten weld puddle. This action decreases with the smaller droplet size. the E indicates an electrode. in E70T-1. For example. and usability factor. Classification of Flux-Cored Electrodes.590 kPa). f. or flux-cored electrode. Due to low penetration and to other properties. the arc appears smoother to the welder. and 1 indicates the chemistry of the deposited weld metal. This explains why there is less visible spatter. the weld deposits have a low sensitivity to cracking. gas type. and the deposition efficiency is higher when the electrode is used at high current rather than at the low end of its current range. Carbon steel electrodes are classified by the American Welding Society specification. This specification includes electrodes having no appreciable alloy content for welding mild and low alloy steels. T indicates tubular. globular transfer. The metal transfer of flux-cored electrodes resembles a fine globular transfer. 70 indicates the required minimum as-welded tensile strength in thousands of pounds per square inch (psi). This is because the covered electrode coating contains binders to keep the coating intact and also contains agents to allow the coating to be extruded.
. the molten droplets build up around the outer sheath of the electrode. Self-Shielding Flux-Cored Electrodes. At low currents. Metal transfer from consumable electrodes across an arc has been classified into three general modes. The system for identifying flux-cored electrodes follows the same pattern as electrodes for gas metal arc welding. Electrodes of this classification are used without externally applied gas shielding and may be used for single-and multiple-pass applications in the flat and horizontal positions. fabricated. d. It is possible for these elements to build up in multipass welds. c. Self-shielding electrodes are usually more voltage-sensitive and require electrical stickout for smooth operation. Some codes prohibit the use of selfshielding wires on steels with yield strength exceeding 42.More flux is used on covered electrodes than in a flux-cored wire to do the same job. "Carbon Steel Electrodes for Flux-cored-Arc Welding". The self-shielding type flux-cored electrode wires include additional gas forming elements in the core. Mild Steel Electrodes. The core material appears to transfer independently to the surface of the weld puddle. and short circuiting transfer.

(8) E70T-6 electrode classification. Due to low penetration. or impact requirements. This classification includes those composite electrodes that are not included in the preceding classes. However. (5) E70T-3 electrode classification. However. multiple-pass welds can be made when the weld beads are heavy and an appreciable amount of mixture of the base and filler metals occurs. The flux-cored electrode wires are considered to be low hydrogen. easily removed slag. and to other properties. (7) E70T-5 electrode classification. and easily controlled and removed slag are characteristics of this class. g. bend test. Welds made using-carbon dioxide shielding gas have better quality than those made with no shielding gas. The E70T-G electrodes are not required to meet chemical. low spatter loss. however. Due to low penetration and to other properties. (3) E70T-1 electrode classification. They may be used with or without gas shielding and may be used for multiple-pass work or may be limited to single-pass applications. high-deposition rate. (4) E70T-2 electrode classification. Electrodes of this classification are used with carbon dioxide shielding gas and are designed primarily for single-pass welding in the flat position and for horizontal fillets. Electrodes of this classification are used without externally applied gas shielding and may be used for single-and multiple-pass applications in the flat and horizontal positions. high-speed welds in the flat and horizontal positions on light plate and gauge thickness base metals. Welding current type is not specified. flatto-slightly convex bead configuration. This classification covers electrodes primarily designed for flat fillet or groove welds with or without externally applied shielding gas. since the materials used in the core do not contain hydrogen. A quiet arc. and a thin. the weld deposits have a low sensitivity to cracking. the weld deposits have a low sensitivity to cracking. radiographic. they are required to meet tension test requirements. slightly convex bead configuration. (9) E70T-G electrode classification. Electrodes of this classification are used without externally applied gas shielding and are intended primarily for depositing single-pass. low penetration. They should not be used on heavy sections or for multiple-pass applications. some of these materials are hydroscopic and thus
.(2) E60T-8 electrode classifications. but are designed for use without an externally applied shielding gas. Electrodes of this classification are used without externally applied gas shielding and may be used for single-and multiple-pass applications in the flat and horizontal positions. Electrodes of this classification are similar to those of the E70T-5 classification. Electrodes of this classification are designed to be used with carbon dioxide shielding gas for single-and multiple-pass welding in the flat position and for horizontal fillets. These electrodes have a globular transfer. (6) E70T-4 electrode classification.

Quality depends on the efficiency of the gas shielding envelope. Flux-cored tubular electrode wires are available which deposit stainless steel weld metal corresponding to the A. Following this and a dash are four-possible suffixes as follows: (1) -1 indicates the use of C02 (carbon dioxide) gas for shielding and DCEP.
. This is followed by the letter T indicating a tubular electrode. flux-cored electrode type and shielding gas. Stainless Steel Tubular Wires. i.W. Electrode wires are packaged in special containers to prevent this. The quality level of of weld metal deposited by the selfshielding type electrode wires is usually lower than that produced by electrodes that utilize external gas shielding. The quality of the deposited weld metal produced by the flux-cored arc welding process depends primarily on the flux-cored electrode wire that is used.I. The deposition rates for flux-cored electrodes are shown in figure 8-2. "Flux-Cored Corrosion Resisting Chromium and Chromium-Nickel Steel Electrodes. This assures the proper matching of base metal. (4) -G indicates that gas shielding and polarity are not specified. It can be expected that the deposited weld metal will match or exceed the properties shown for the electrode used. Flux-cored electrodes have a much broader current range than covered electrodes. These electrodes are covered by the A.S specification. These curves show deposition rates when welding with mild and low-alloy steel using direct current electrode positive. Two type of of covered electrodes are shown for comparison. (2) -2 indicates the use of argon plus 2 percent oxygen for shielding and DCEP. These electrode wires must be stored in a dry room. Deposition Rates and Weld Quality.S.I. The metal utilization of the flux-cored electrode is higher. on the cleanliness of the joint." These electrodes are identified by the prefix E followed by the standard A.I.I. code number. (3) -3 indicates no external gas shielding and DCEP. compositions. Tubular or flux-cored electrode wires are also used for surfacing and submerged arc welding applications. Deposition rates of the smaller size flux-cored wires exceed that of the covered electrodes.S. h. and on the skill of the welder. on the joint detail. which increases the flexibility of the process.tend to absorb moisture when exposed to a high-humidity atmosphere.

NONCONSUMABLE ELECTRODES a. 8-5.Section II. and brazing alloys. and other materials. flux additives. There are also ferrules used for stud welding and the guide tubes in the consumable guide electroslag welding method. GENERAL There are other filler metals and special items normally used in making welds. Another type of material consumed in making a weld are the consumable rings used for root pass welding of pipe. OTHER FILLER METALS
8-4. consisting of a
. There are two types of nonconsumable electrodes. solders. Types of Nonconsumable Electrodes. including backing tapes. The carbon electrode is a non-filler metal electrode used in arc welding or cutting. backing devices. Other filler materials are solders and brazing alloys. These include the nonconsumable electrodes (tungsten and carbon).

Applications include carbon arc welding. It provides diameter information.0.3 to 0. (5) Tungsten electrodes containing 0. tungsten containing 2.3 to 0.0 or 2.1.0 percent thorium.5 percent zirconium. They are also used for plasma-arc and atomic hydrogen arc welding. they must be operated at maximum current density to obtain reasonable arc stability. 5 percent tungsten) electrodes are generally used on less critical welding operations than the tungstens which are alloyed.0 percent thorium. (b) Yellow . MIL-E-17777C. Tungsten Electrodes. and tungsten containing 0. longer life. 8-3). and copper coated. carbon cutting. (1) Nonconsumable electrodes for gas types: pure tungsten.5 percent zirconium.3 to 0.0 percent thorium) are superior to pure tungsten electrodes because of their higher electron output. entitled. twin carbon arc welding.pure tungsten. Tungsten electrode points are difficult to
. c.2. and greater resistance to contamination. "Electrodes Cutting and Welding Carbon-Graphite Uncoated and Copper Coated". better arc starting and arc stability. Carbon Electrodes.5 percent zirconium generally fall between pure tungsten electrodes and thoriated tungsten electrodes in terms of performance. quality assurance. made principally of tungsten. There is. The American Welding Society does not provide specification for carbon electrodes but there is a military specification. and requirements for size tolerances. sampling. This type of electrode has a relatively low current carrying capacity and a low resistance to contamination. and air carbon arc cutting and gouging. (4) Thoriated tungsten electrodes (1. defined as a non-filler metal electrode used in arc welding or cutting. and various tests. no. uncoated.carbon graphite rod which may or may not be coated with copper or other coatings. When electrodes are not grounded. high current-carrying capacity. some indication of better performance in certain types of welding using ac power. b. (d) Brown . (c) Red . length information. however. This specification provides a classification system based on three grades: plain. (6) Finer arc control can be obtained if the tungsten alloyed electrode is ground to a point (fig.0 percent thorium. (2) Tungsten electrodes can be identified by painted end marks: (a) Green . (3) Pure tungsten (99. The second nonconsumable electrode is the tungsten electrode.0 percent thorium. tungsten containing tungsten arc (TIG) welding are of four 1.

Unless high frequency alternating current is available. (0. indicating the benefit derived by using the particular additive.32 cm) might be used for butt joints in light gauge material. some of which include small amounts of flux. the electrode must be removed. and replaced in the torch. Backing materials are being used more frequently for welding. the additives are of a proprietary nature and are described by their manufacturers. If contamination does occur. an extension beyond the gas cup of 1/8 in. Additives are provided to increase productivity or enrich the alloy composition of the deposited weld metal. These are rings made of metal that are tack welded in the root of the weld joint and are fused into the joint by the gas tungsten arc. There are three basic types of rings called consumable inert rings which are available in different analyses of metal based on normal specifications.64 to 1. which can be used for backing the roots of joints. the manufacturer's information must be used. 8-6. reground. Special tapes exist. SUBMERGED ARC FLUX ADDITIVES Specially processed metal powder is sometimes added to the flux used for the submerged arc welding process. touch-starting must be used with thorium electrodes. This process gives greater strength and will withstand more heat
. (0.maintain if standard direct current equipment is used as a power source and touch-starting arc is standard practice. Since there are no specifications covering these types of materials. and hard soldering is called silver solder brazing. for one-side welding. Hard solders are called spelter. d. 8-7. The tungsten electrode or torch should be inclined slightly and the filler metal added carefully to avoid contact with the tungsten to prevent contamination of the electrode. Consumable rings are used for making butt welds in pipe and tubing.
(7) The electrode extension beyond the gas cup is determined by the type of joint being welded. Backing Materials. The kind of solder used depends on the metals being joined.27 cm) might be necessary on some fillet welds. Tungsten electrodes alloyed with thorium retain their shape longer when touch-starting is used. while an extension of approximately 1/4 to 1/2 in. There are also different composite backing materials. SOLDERING a. For example. Maintenance of electrode shape and the reduction of tungsten inclusions in the weld can best be ground by superimposing a high-frequency current on the regular welding current. In both cases. General. Soldering is the process of using fusible alloys for joining metals.

Soft soldering is used for joining most common metals with an alloy that melts at a temperature below that of the base metal. Solders of the tin-lead alloy system constitute the largest portion of all solders in use. tin-silver.than soft solder. zinc-aluminum. These are described below. or an increase of the zinc content to as high as 40 percent. bismuth (fusible) solder. Alloys containing 70 to 80 percent tin with the balance zinc are recommended for soldering aluminum. For its strength. and heating may be used. cadmium-zinc. The addition of 1 to 2 percent aluminum. The addition of silver also increases creep strength. The 91/9 and 60/40 tin-zinc solders may be used for high temperature applications (above 300°F (149°C)). (2) Tin-antimony-lead solders. and creep strengths and are recommended for cryogenic applications. tin-lead-silver. improves corrosion resistance. A large number of tin-zinc solders have come into use for joining aluminum. in that the base is not melted. (4) Tin-zinc solders. cadmium-silver. In many respects. the liquidus temperature rises correspondingly. Other solders are: tinantimony. and excellent flow characteristics. only inorganic fluxes are recommended for use with these solders. The 62 percent tin-38 percent lead-2 percent silver solder is used when soldering silver-coated surfaces for electronic applications. Galvanic corrosion of soldered joints in aluminum is minimized if the metals in the joint are close to each other in the electrochemical series. while the 80/20 and the 70/30 tin-zinc solders are generally used to coat parts before soldering. The high lead solders containing tin and silver provide higher temperature solders or many applications. However. tin-antimony-lead. CAUTION
. the choice depends on the base metal to be joined. the solder is used many plumbing. shear. the soldered joint depends on the penetration of the solder into the pores of the base metal and. tin-zinc. (1) Tin-antinmony solder. Fluxes of all types can also be used. but merely tinned on the surface by the solder filler metal. b. The addition of antimony up to 6 percent of the tin content increases the mechanical properties of the solder with only slight impairment to the soldering characteristics. The 95 percent tin-5 percent antimony solder provides a narrow melting range at a temperature higher than the tin-lead eutectic. refrigeration. and indium solders. All standard methods of cleaning. the formation of a base metal-alloy solder. Most cleaning and soldering processes may be used with the tin-lead solders. and air conditioning applications because of its good creep strength. and these solders are therefore more difficult to apply. They exhibit good tensile. this is similar to brazing. They are used for joining most metals and have good corrosion resistance to most materials. It has good shape and creep strengths. and always below 800°F (427°C). The 96 percent tin-4 percent silver solder is free of lead and is often used to join stainless steel for food handling equipment. fluxing. Antimony may be added to a tin-lead solder as a substitute for some of the tin. The silver addition retards the dissolution of the silver coating during the soldering operation. (3) Tin-silver and tin-lead-silver solders. Because of their high melting range.

they are not effective below 350°F (177°C). Strong. The 95 percent cadmium-5 percent silver solder is in applications where service temperatures will be higher than permissible with lower melting solders. Particular attention must be paid to the cleanliness of metal surfaces. and on temperature-sensing devices. (5) Cadmium-silver solder. a tensile strength of 18 MPa (2600 psi) can be obtained. are very difficult to use successfully in high-speed soldering operations. Improper use of solders containing cadmium may lead to health hazards. particularly with respect to fume inhalation. soldering joints where adjacent material is very sensitive to temperature and would deteriorate at higher soldering temperatures. The low melting temperature solders have applications in cases such as soldering heat treated surfaces where higher soldering temperatures would result in the softening of the part. however. A 50 percent indium-50 percent tin alloy adheres to glass
. Improper use of solders containing cadmium can be hazardous to personnel. Improper use of this solder may lead to health hazards. Joining aluminum to itself or to other metals is possible with this solder. such as copper or steel. care should be taken in their application. (7) Zinc-aluminum solder. Ultrasonic solder pots are employed without the use of flux. At room temperature. (6) Cadmium-zinc solders. Therefore. These solders possess certain properties which make them valuable for some special applications. where the device is activated when the fusible alloy melts at relatively low temperature. Bismuth-containing solders. Their usefulness for any particular application should be checked with the supplier. In manual operations. (8) Fusible alloys. A major application is in dip soldering the return bends of aluminum air conditioner coils. Many of these solders. which limits its use to applications where soldering temperature is in excess of 700°F (371°C) can be tolerated. butt joints in copper can be made to produce tensile strengths of 170 MPa (25. If the surface can be plated for soldering with such metals as tin or tin-lead.000 psi). are useful for soldering operations where soldering temperatures helm 361°F (183°C) are required. (9) Indium solders. noncorrosive rosin fluxes may be satisfactory.Cadmium fumes can be health hazards. particularly with respect to fume inhalation. the heated aluminum surface is rubbed with the solder stick to promote wetting without a flux. These solders are also useful for soldering aluminum. corrosive fluxes must be used to make satisfactory joints on uncoated surfaces of metals. such as fire sprinkler systems. step soldering operations where a low soldering temperature is necessary to avoid destroying a nearby joint that has been made with a higher melting temperature solder. The solidus temperature is high. the fusible alloys. The 40 percent cadmium-60 percent zinc solder has found considerable use in the soldering of aluminum lamp bases. particularly those containing a high percentage of bismuth. This solder is specifically for use on aluminum. At 425°F (218°C). It develops joints with high strength and good corrosion resistance. The cadmium-zinc solders develop joints with intermediate strength and corrosion resistance when used with the proper flux.

melt at a temperature so near to that of the filler rod that fusion welding rather than brazing is required. (3) A composition of sufficient homogeneity and stability to minimize separation of constituents (liquation) under the brazing conditions encountered. (3) The choice of the filler metal depends on the types of metals to be joined. Some of these brasses and bronzes. nickel. They should be chemically active and fluid at the brazing temperature. In brazing. Characteristics.
. but stove 800°F (427°C) is used. a filler metal of the required composition and a proper flux are important to the success of any brazing operation. and techniques used with the tin-lead solders are applicable to iridium solders. The low vapor pressure of this alloy makes it useful for seals in vacuum systems. a nonferrous filler rod. Iridium solders do not require special techniques during use. an even coating of flux should be brushed over the adjacent surfaces of the joint. or wire is used for repairing or joining cast iron. b. plug. steel. (2) A melting point or melting range compatible with the base metals being joined and sufficient fluidity at brazing temperature to flow and distribute into properly prepared joints by capillary action. and high melting point brasses and bronzes. malleable iron. taking care that no spots are left uncovered. (1) Brazing is similar to the soldering processes in that a filler rod with a melting point lower than that of the base metal. and to promote the free flowing of the filler metal. A groove.readily and may be used for glass-to-metal and glass-to-glass soldering. (2) Besides a welding torch with a proper tip size. Copper-tin (phosphor-bronze) rods are used for brazing similar copper alloys and for brazing steel and cast iron. For satisfactory use in brazing applications. General. fillet. brazing filler metals must possess the following properties: (1) The ability to form brazed joints possessing suitable mechanical and physical properties for the intended service application. fluxes. copper. wrought iron. 8-8. BRAZING ALLOYS a. strip. (4) Fluxes are used to prevent oxidation of the filler metal and the base metal surface. All of the soldering methods. however. Coppersilicon (silicon-bronze) rods are used for brazing copper and copper alloys. After the joint members have been fitted and thoroughly cleaned. The proper flux is a good temperate indicator for torch brazing because the joint should be heated until the flux remains fluid when the torch flame is momentarily removed. or slot weld is made and the filler metal is distributed by capillary attraction. Other compositions are used for brazing specific metals.

. washers. thermal cycling.). or to promote removal of certain refractory oxides by vacuum or an atmosphere. c. shims. or allow the introduction of the brazing filler metal after the base metal reaches the brazing temperature. Low brazing temperatures are usually preferred to economize on heat energy. or heat treatment of the base metal with brazing. formed wires. grain growth. and increase the life of fixtures and other teals. Such alloys may also be manually or automatically face fed into the joint after the base metal is heated. but more economical. Flux should be used in all cases and removed after brazing. sound bond. and vacuum operation. High brazing temperatures are preferred in order to take advantage of a higher melting. to combine annealing.(4) The ability to wet the surfaces of the base metals being joined and form a strong. (4) Method of heating. Filler metals with narrow melting ranges (less than 50°F (28°C) between solidus and liquidus) can be used with any heating method. The following factors should be considered when selecting a brazing filler metal: (1) Compatibility with base metal and joint design. to permit subsequent processing at elevated temperatures. ability to produce or avoid base metal-filler metal interactions. brazing filler metal. Brazing sheet or tubing is frequently used as one member of an assembly with the mating piece made of an unclad brazeable alloy. corrosive conditions. They are suited for furnace and dip brazing. such as service temperature (high or cryogenic). to promote base metal-filler metal interactions to increase the joint remelt temperature. life expectancy. The coating on the brazing sheet or tubing melts at brazing temperature and flows by capillary attraction and gravity to fill the joints. Compositions should be selected to suit operating requirements. Filler Metal Selection. warpage. etc. minimize heat effects on base metal (annealing. (5) Depending on the requirements. while some types are also suited for torch brazing using lap joints rather than butt joints. minimize base metal-filler metal interaction. and the brazing filler metal may be preplaced in the joint area in the form of rings. (2) Service requirements for the brazed assembly. powder. This group is used for joining aluminum and aluminum alloys. d. Aluminum-Silicon Filler Metals. (3) Brazing temperature required. Filler metals that tend to liquate should be used with heating methods that bring the joint to brazing temperature quickly. except when vacuum brazing. stress loading. The coatings are aluminum-silicon alloys and may be applied to one or both sides of sheet. radiation stability. or paste. Use brazing sheet or tubing that consists of a core of aluminum alloy and a coating of lower melting filler metal to supply aluminum filler metal. stress relief.

flux is recommended with all other metals. A mineral flux is commonly used with the filler metals. dry argon. is used for the AZ31B and ZE10A compositions. one magnesium filler metal (BMg-1) is used for joining AZ10A. Magnesium Filler Metals. Heating must be closely controlled with both filler metals to prevent melting of the base metal. However. However. Copper and Copper-Zinc Filler Metals. or furnace brazing processes. nickel base. nickel and nickel base alloys. and induction brazing processes. (2) Copper-zinc alloy filler metals are used on most common base metals. copper filler metals are available in wrought and powder forms. g. copper-nickel alloys. (3) Copper-zinc filler metals are used on steel. h. Both filler metals are suited for torch. (1) The essentially pure copper brazing filler metals are used for joining ferrous metals. or on copper-nickel alloys with more than 10 percent nickel. hydrogen.e. and combusted fuel gas). These filler metals are primarily used for joining copper and copper alloys and have some limited use for joining silver. with metals that have components with difficult-to-reduce oxides (chromium. titanium. silicon bronze. or stainless steel. They are used with the torch. dip. a higher quality atmosphere or mineral flux may be required. and a borax-boric acid flux is commonly used. including copper alloys. KIA. However. copper alloys. Because of its higher melting range. while the other alloy (BMg-2a). with all methods of heating. They are commonly used for lap and butt joints with various brazing processes. copper. These filler metals are suited for all brazing processes and have self fluxing properties when used on copper. manganese. vacuum. CAUTION
. and copper-nickel alloys. They should not be used on ferrous or nickel base alloys. f. with a lower melting range. and stainless steel where corrosion resistance is not a requirement. but fluxless brazing with filler metals free of cadmium and zinc can be done on most metals in an inert or reducing atmosphere (such as dry hydrogen. and MIA magnesium alloys. They may be prep laced in the joint or fed into the joint area after heating. silicon. except aluminum and magnesium. They are very free flowing and are often used in furnace brazing with a combusted gas. furnace. Silver Filler Metals. and aluminum). vanadium. tungsten. or dissociated ammonia atmosphere without flux. (1) These filler metals are used for joining most ferrous and nonferrous metals. Fluxing is required. These brazing filler metals are used for joining various ferrous metals and nonferrous metals. Copper-Phosphorus Filler Metals. Fluxes are generally required. the corrosion resistance of the copper-zinc alloy filler metals is generally inadequate for joining copper. and molybdenum.

i. it is preferred to tin. (3) Of the elements that are commonly used to lower the melting and flow temperatures of copper-silver alloys. Cadmium oxide fumes are hazardous. furnace. cemented carbides. (4) Tin has a low vapor pressure at normal brazing temperatures. (5) Stellites. cobalt. These filler metals are used for joining parts in electron tube assemblies where volatile components are undesirable. and the brazing of iron. Lithium is capable of reducing the adherent oxides on the base metal. (6) When stainless steels and other alloys that form refractory oxides are to be brazed in reducing or inert atmospheres without flux. Alloys containing zinc wet ferrous metals more effectively than those containing tin. Lithium bearing alloys are advantageously used in very pure dry hydrogen or inert atmospheres. and where zinc is tolerable. Alone or in combination with cadmium or tin. If they are improperly used and subjected to overheating. They are particularly recommended where joints in stainless steel are to be exposed to salt water corrosion. Because of their low rate of interaction with the base metal. a borax-boric acid flux may be used. and excessive inhalation of these fumes must be avoided. and infrequently. and cobalt base metals where resistance to oxidation or corrosion is required. and other molybdenum and tungsten rich refractory alloys are difficult to wet with the alloys previously mentioned. Cadmium bearing filler metals should be used with caution. are often added as wetting agents in brazing filler metals for joining these materials. zinc is by far the most helpful wetting agent when joining alloys based on iron. Nickel Filler Metals. nickel. nickel.
. Manganese. usually with induction. or when the brazed assemblies will be used in high vacuum at elevated temperatures.Do not overheat filler metals containing cadmium. The resultant lithium oxide is readily displaced by the brazing alloy. An important characteristic of silver brazing filler metals containing small additions of nickel is improved resistance to corrosion under certain conditions. j. or nickel. Tin additions to silver-copper alloys produce filler metals with wide melting ranges. such as when brazing is done without flux in atmosphere or vacuum furnaces. (2) The addition of cadmium to the silver-copper-zinc alloy system lowers the melting and flew temperatures of the filler metal. or resistance heating in a reducing atmosphere or in vacuum without flux. cobalt. Gold Filler Metals. For certain applications. they are commonly used on thin sections. silver brazing filler metals containing lithium as the wetting agent are quite effective. cadmium oxide frees can be generated. Cadmium also increases the fluidity and wetting action of the filler metal on a variety of base metals. Cadmium oxide fumes are a health hazard. It is used in silver brazing filler metals in place of zinc or cadmium when volatile constituents are objectionable. zinc produces alloys that wet the iron group metals but do not alloy with them to any appreciable depth.

brazing should be performed in a high quality atmosphere. is warranted in those cases. The use of brazing to join these materials is somewhat restricted by the lack of filler metals specifically designed for brazing them. copper and silver base filler metals may be used. copper-phosphorus. Other base metals such as carbon steel. These filler metals are limited in their applications.
. gold-nickel. Cobalt Filler Metal. because they cannot operate at very high temperatures. (3) A wide variety of brazing filler metals may be used to join molybdenum. Special high temperature fluxes are available. The filler metals are normally applied as powders. and 2200°F (1204°C) short time service. This filler metal is generally used for its high temperature properties and its compatibility with cobalt base metals. and copper. The service temperature requirement in many cases dictates the brazing filler metal selection. time should be kept as short as possible. They are generally used on 300 and 400 series stainless steels and nickel and cobalt base alloys. When high temperature service is not required. Although several references to brazing are present. The use of higher melting metals. Higher melting metals and alloys may be used as brazing filler metals at still higher temperatures. The filler metals also exhibit satisfactory room temperature and cryogenic temperature properties down to the liquid point of helium. The quantity of filler metal and time at brazing temperatures should be controlled because of the high solubility of some base metals in these filler metals. For optimum results. When brazing above the recrystallization temperature. Nickel base and precious-metal base filler metals may be used for joining tungsten. the reported filler metals that are suitable for applications involving both high temperature and high corrosion are very limited. Each filler metal should be evaluated for its particular applicability. gold-copper.(l) These brazing filler metals are generally used for their corrosion resistance and heat resistant properties up to 1800°F (982°C) continuous service. such as tantalum and columbium. and copper are also brazed when specific properties are desired. k. such as silver-copper-zinc. (1) Brazing is an attractive means for fabricating many assemblies of refractory metals. (2) The phosphorus containing filler metals exhibit the lowest ductility because of the presence of nickel phosphides. and copper-nickel filler metals can be used. low alloy steels. depending on the specific filler metals and operating environment. For electronic parts and other nonstructural applications requiring higher temperatures. or in the form of sheet or rod with plastic binders. pastes. However. however. The boron containing filler metals should not be used for brazing thin sections because of their erosive action. Filler Metals for Refractory Metals. consideration must -be given to the effect of brazing temperature on the base metal properties. (2) Low melting filler metals. in particular those involving thin sections. 1. are used to join tungsten for electrical contact applications. The brazing temperature range is the same as that for tungsten. specifically recrystallization.

. Filler metal specifications and welding processes are shown in table 8-2.(4) Copper-gold alloys containing less than 40 percent gold can also be used as filler metals. m. Although silver base filler metals have been used to join tantalum and columbium. but gold content between 46 and 90 percent tends to form age hardening compounds which are brittle. they are not recommended because of a tendency to embrittle the base metals.

.

as well as the assembled equipment are thoroughly tested before the material is issued to the using services in the field. b. (3) Determine the type of metal used in the damaged part. most of the damage to and failures of the equipment are due to accidents. Appendix A contains references to formal DA publications covering additional equipment used by military item and other equipment not covered by standard welding procedures as set forth in other chapters of this manual. what heat treatment was used. b. armor. SIZING UP THE JOB a. it must be determined whether or not the materiel can be satisfactorily welded. (1) Determine the nature and extent of the damage and the amount of straightening and fitting of the metal that will be required. Appendix A also contains references to formal DA publications covering additional equipment used by military personnel which are not included in this chapter. whether it was heat treated. Determination of Weldability. This determination is based upon the factors listed below.CHAPTER 9 MAINTENANCE WELDING OPERATIONS FOR MILITARY EQUIPMENT
9-1. SCOPE
a. 9-2. c. and heavy structural work are covered in chapter 12. and if so. overloading. section VII of this circular. It is in this class of repair work that field service welding is utilized most frequently. or unusual shocks for which the equipment was not designed to withstand. All of the materials used in the manufacture of military materiel. Before repairing any damaged materiel.
. This chapter contains information necessary to determine the size of the welding job and proper welding procedures for military items. low alloy structural steels (such as TI) used for bulldozer blades. Therefore. General. Welding techniques for equipment containing high yield strength. (2) Determine the possibility of restoring the structure to usable condition without the use of welding. (4) Determine if the welding heat will distort the shape or in any manner impair the physical properties of the part to be repaired.

Successful welded repairs cannot be made on machined parts that carry a dynamic load. A thorough working knowledge of these processes and
. Repairing Heat Treated Parts. even though the weld metal deposited has good properties. Welding operations on ordnance materiel are restricted largely to those parts whose essential physical properties are not impaired by the welding heat. springs. by test procedures as described in chapter 7. (1) In emergency cases. piston rods. valves. These electrodes will produce a satisfactory weld. or from assembly drawings of the components. or both. IDENTIFYING THE METAL Welding repairs should not be made until the type of metal used for the components or sections to be repaired has been determined. DETERMINING THE WELDABLE PARK a. or toughness. SELECTING THE PROPER WELDING PROCEDURES The use of welding equipment and the application of welding processes to different metals is covered in other chapters of this manual.(5) Determine if heat treating or other equipment or materials will be required in order to make the repair by welding. c. b. c. This information can be obtained by previous experience with similar materiel. In any of these repairs. 9-4. depending on their application in service. although a narrow zone in the base metal in the vicinity of the weld will be affected by the heat of welding. hardness. requires the annealing of the broken part and welding with a high strength rod. 9-3. This method produces a welded joint that can be heat treated. This method should not be attempted unless proper heat treating equipment is available. (3) The preferred metal of repairing heat treated steels. and cam are considered to be unsuitable for field welding because welding heat alters or destroys the heat treatment of these parts. These drawings should be carried by maintenance companies in the field and should show the type of material and the heat treatment of the parts. some heat treated parts can be repaired in the heat treated condition by welding with stainless steel electrodes containing 25 percent chromium and 20 percent nickel. the heat treated part will lose some of its strength. The entire part should be heat treated after welding to obtain the properties originally found in the welded parts. antifriction bearings. This applies particularly to high alloy steels that are heat treated for hardness or toughness. when practicable. 9-5. pistons. shafts. (2) Minor defects on the surface of heat treated parts may be repaired by either hard surfacing or brazing. or an 18 percent chromium-8 nickel electrode containing manganese or molybdenum. Gears. connecting rods.

Drain the fuel tank and close the fuel and oil tank shut off valves. d. d. tack welding. and preheating must be determined. of necessity. A reinforcement must be designed that will provide the required strength without producing high local rigidity or excessive weight. and flame adjustment must be determined. Be familiar with and observe the safety precautions prescribed in chapter 2 of this circular. In preparing the edges of plates or parts to be welded. If a gas welding process is used.metals is necessary before a welding procedure for any given job can be selected. and proper cooling procedure. Military materiel is designed for lightness and the safety factors are. prepare them for welding in accordance with the instructions in chapter 2. The need for backing strips. tip size. correct gas pressure. PRELIMINARY PRECAUTIONS Before beginning any welding or cutting operations on the equipment. flux. the proper cleaning and beveling of the parts to be joined must be considered. e. This necessitates sane reinforcement at the joint to compensate for the strength lost in the welded part due to the welding heat. the proper type of welding rod.
. a. spacing of the parts to permit some movement. When it has been decided by competent authority that the repair can be made by welding. quench plates. or about the vehicle or materiel. c. Remove all ammunition from. the safety precautions listed below must be considered. If welding or cutting is to be done on the tanks. Reducing warping and internal stresses requires the use of the proper sequence for welding. the factors outlined below must be considered. section V. b. must be determined if an arc welding process is used. together with the current and polarity setting. on. control and proper distribution of the welding heat. low in some cases. b. 9-6. a. Keep heat away from optical elements. Have a fire extinguisher nearby. control of the size and location of the deposited weld metal beads. The proper type and size of electrode. c.

Welds are made with or without the application of pressure and with or without filler metals. Weld Metal Deposition. is vaporized. twin carbon-arc welding. b. In other positions. In the arc welding process. Arc welding processes that fall into this category include carbonarc welding. stud welding. GENERAL
10-1. DEFINITION OF ARC WELDING a. as the surface tension is unable to retain a large amount of molten metal in the weld crater. Gravity affects the transfer of metal in flat position welding. between two electrodes. A small part of the metal passing through the arc. In metal-arc welding. arc spot welding. Arc welding processes may be divided into two classes based on the type of electrode used: metal electrodes and carbon electrodes. gas metal-arc welding. small electrodes must be used to avoid excessive loss of weld metal. Arc welding processes that fall into this category include bare metal-arc welding.CHAPTER 10 ARC WELDING AND CUTTING PROCESS
Section I. Some of this vaporized metal escapes as spatter. gas tungsten arc welding. but most of it is condensed in the weld crater. (4) Pinch effect. (3) Gravity. or in some cases. gas shielded stud welding. This occurs with all types of electrodes and in all welding positions. The high current passing through the molten metal at the tip of the electrode sets up a radial compressive magnetic force that tends to pinch the molten globule and detach it from the electrode. shielded metal-arc welding. gas carbon-arc welding.
. Definition. which is at a much lower temperature. atomic hydrogen welding. the weld is produced by the extreme heat of an electric arc drawn between an electrode and the workpiece. Detailed descriptions of the various processes may be found in chapter 6. (2) Carbon electrodes. a number of separate forces are responsible for the transfer of molten filler metal and molten slag to the base metal. especially the metal in the intense heat at the end of the electrode. and arc seam welding. These forces are described in (2) through (7) below. and shielded carbon-arc welding. (1) General. submerged arc welding. (2) Vaporization and condensation. (1) Metal electrodes. paragraph 6-2.

The static output characteristic curve produced by both sources is shown in figure 10-1. the constant voltage machine. According to this theory of metal movement in the welding arc.
. steel that has been almost completely deoxidized in casting) cannot he used successfully in the overhead position.. carbon monoxide is evolved within the molten metal at the electrode tip. 10-2. This theory is substantiated by the fact that bare wire electrodes made of high purity iron or "killed steel" (i. This force holds filler metal and the slag globules in contact with the molten base or weld metal in the crater. forming a low spot. Gases are produced by the burning and volatilization of the electrode covering and are expanded by the heat of the boiling electrode tip. The velocity and movement of this gas stream give the small particles in the arc a movement away from the electrode tip and into the molten crater on the work. causing miniature explosions which expel molten metal away from the electrode and toward the work.e. Two basic types of power sources are expressed by their voltage-ampere output characteristics. WELDING WITH CONSTANT CURRENT The power source is the heart of all arc welding process. (6) Gas stream from electrode coatings. the spatter. The other power source. The constant current machine is considered in this paragraph. The characteristic curve of a welding machine is obtained by measuring and plotting the output voltage and the output current while statically loading the machine. is discussed in paragraph 10-3. The metal transfer from electrode to the work. causes the edges to cool first. caused by the decarburizing action in molten steel.(5) Surface tension. It has little to do with the transfer of metal across the arc. (7) Carbon monoxide evolution from electrode. c. and the crater formation are. but is an important factor in retaining the molten weld metal in place and in the shaping of weld contours. forcing the liquid metal towards the edges of the crater. in this theory. Arc craters are formed by the pressure of expanding gases from the electrode tip (arc blast). Arc Crater. The higher temperature of the center. Metal is thus drawn from the center to the edges. as compared with that of the sides of the crater.

(fig. It also has a static voltampere curve that tends to produce a relatively constant output current.a. and has been used for many years for the shielded metal arc welding process. or the variable voltage type. The conventional or constant current (CC) type power source may have direct current or alternating current output. gas tungsten arc welding. If the arc length varies because of external influences. It is used for the shielded metal-arc welding process. The shaded area is the normal arc voltage range. a large number of output curves can be obtained. When a nonconsumable electrode is used. which is usually greater than the rated output of the machine. continuously fed consumable electrodes. The conventional machine is known as the constant current (CC) machine. With tap or plug-in machines. There are two control systems for constant current welding machines: the single-control machine and the dual-control machine. The characteristic volt-ampere curve is shown by figure 10-2. 10-1). The dotted lines show intermediate adjustments of the machine. By adjusting the current control. the number of covers will correspond to the number of taps
. It is used for stud welding and can be used for the continuous wire processes when relatively large electrode wires are used. carbon arc welding and gouging. and slight changes in the arc voltage result. The arc voltage. is responsive to the rate at which a consumable electrode is fed into the arc. The CC machine has the characteristic drooping volt-ampere curve. the welding current remains constant. at a given welding current. A constant-current arc-welding machine is usually used with welding processes which use manually held electrodes. (1) The single-control machine has one adjustment which changes the current output from minimum to maximum. the arc voltage is responsive to the electrode-towork distance. b. and plasma arc welding. A constant-current arcwelding machine is one which has means for adjusting the arc current. or nonconsumable electrodes. c.

The slope is changed by changing the open-circuit voltage with the fine-current control adjustment knob. They have two adjustments. However. The slope of the characteristic curve can be changed from a shallow to a steep slope according to welding requirements. Figure 10-3 shows some of the different curves that can be obtained. it is difficult to strike an arc. Generator welding machines usually have dual controls. this adjustment does not change arc voltage. which also acts as an open-circuit voltage adjustment. Most transformer and transformer-rectifier machines are single-control welding machines. The fine-current control will change the open-circuit voltage from approximately 55 volts to 85 volts.or plug-in combinations available. one for coarse-current control and the other for fine-current control.
. Other curves are obtained with intermediate open-circuit voltage settings. when welding. These machines inherently have slope control. The open-circuit voltage affects the ability to strike an arc. If the opencircuit voltage is much below 60 volts.
(2) Dual control machines have both current and voltage controls. The coarse adjustment sets the current output of the machine in steps from the minimum to the maximum current. They offer the welder the most flexibility for different welding requirements. Arc voltage is controlled by the welder by changing the length of the welding arc.

the long arc (high voltage) is a lower current arc. the current is reduced. With the same machine setting. This allows the welder to control the size of the molten puddle while welding. This is illustrated by figure 10-4. the power source produces more current. and the puddle freezes quicker. which provides the control needed for out-of-position work. This type of control is built into conventional constant current type of machine. the power source provides less welding current. The amount of molten metal is reduced. While welding. A short arc has lower voltage and the long arc has higher voltage. the arc spreads out. Conversely. the short arc (lower voltage) is a high-current arc. With a short arc (lower voltage). which shows three curves of arcs and two characteristic curves of a dual-control welding machine. The operating point changes continuously during welding. a normal arc. and the lower curve is for a short arc. and without changing the control on the machine. The arc length can vary. When the welder purposely and briefly lengthens the arc. single-or dual-control.(a) The different slopes possible with a dual-control machine have an important effect on the welding characteristic of the arc. The intersection of a curve of an arc and a characteristic curve of a welding machine is known as an operating point. depending on the welding technique. and with a longer arc (higher voltage). The three arc curves are for a long arc.
. the welder can lengthen or shorten the arc and change the arc voltage from 35 to 25 volts. ac or dc.

The top curve shows an 80-volt open-circuit voltage and the bottom curve shows a 60volt open-circuit voltage. and each allows a different current change for the same arc voltage change. The flatter slope curve provides a digging arc where an equal change in arc voltage produces a greater change in arc current. The dual-control generator welding machine is the most flexible of all types of welding power sources. The steeper slope curve has less current change for the same change in arc length and provides a softer arc.
. the voltage and current relationship will stay on the same curve or line. This ability to control the current in the arc over a fairly wide range is extremely useful for making pipe welds. Both curves in figure 104 are obtained on a dual-control machine by adjusting the fine control knob. the current increases. Consider first the 80-volt opencircuit curve which produces the steeper slope. With either adjustment. the welding current will increase almost twice as much as it did when following the 80-volt open-circuit curve. 60-volt open-circuit curve. With the flatter. less penetrating arc by changing the arc length.(b) With the dual-control machine. since it allows the welder to change to a higher-current arc for deep penetration or to a lower-current. This is the advantage of a dual-control welding machine over a single-control type. There are many characteristic curves between the 80 and 60 open circuit voltage curves. The welder manipulates the arc. the welder can adjust the machine for more or less change of current for a given change of arc voltage. When the arc is long with 35 volts and is shortened to 25 volts. This is done without touching the machine control. when the arc is shortened from 35 volts to 25 volts. since the slope of the curve through the arc voltage range is adjustable only on a dual-control machine.

Pulsed arc is very useful when welding with the gas tungsten arc welding process. This is a great advantage for gas tungsten arc welding. though not as flexible as the dual-control motor generator. produces direct current for welding. which can be programmed to change from a high current (HC) to a low current (LC) on a repetitive basis. the output of the machine continuously switches from the high to the low current as shown in figure 10-6. The rectifier welding machine. there is voltage present which helps to re-establish the arc quickly. This gives the welder the necessary control over the arc and weld puddle. the length of time for the high and low current pulses is adjustable. The constant-current power supplies are rarely used for very small electrode wire welding processes. according to line frequency or at each current reversal. since the working arc length of the tungsten arc is limited. Alternating current for welding is usually produced by a transformer type welding machine. it is necessary to be able to change the current level while welding. This is done by the machine. Pulsed current welding is useful for shielded metal-arc welding of pipe when using certain types of electrodes. These machines are essentially single-control machines and have a static volt ampere output characteristic curve similar to that shown in figure 10-4 above. Arc welding machines have been developed with true constant-current volt-ampere static characteristics. These machines. but because of the phase difference. within the arc voltage range. sometimes called background current.d. The difference between alternating and direct current welding is that the voltage and current pass through zero 100 or 120 times per second. By programming a control circuit. to obtain weld puddle control. In addition. This requires a complex system with feedback from the arc voltage to compensate for changes in the arc length.
. although engine-driven alternating current generator welding machines are available for portable use. The static volt ampere characteristic curve of an alternating current power source the same as that shown in figure 10-4 above. the arc is extinguished. Reactance designed into the machine causes a phase shift between the voltage and current so that they both do not go through zero at the same instant. The degree of ionization in the arc stream affects the voltage required to re-establish the arc and the overall stability of the arc. Arc stabilizers (ionizers) are included in the coatings of electrodes designed for ac welding to provide a stable arc. f. since the welding current remains the same whether the arc is short or long. e. A welder using this type of machine has little or no control over welding current by shortening or lengthening the arc. The wire feeder and control must duplicate the motions of the welder to start and maintain an arc. Some transformer welding power sources have fine and coarse adjustment knobs. This is a great advantage for gas tungsten current by shortening or lengthening the arc. g. The slope of the volt-ampere curve through the welding range is generally midway between the maximum and minimum of a dualcontrol machine. but these are not dual control machines unless the open-circuit voltage is changed appreciably. When the current goes through zero. In shield metal-arc welding. since the welding current remains the same whether the arc is short or long. technically known as the transformer-rectifier. known as pulsed welding. The level of both high and low current is adjustable. as shown by figure 10-5. can be used for all types of shielded metal arc welding where direct current is required. The constant-current type welding machine can be used for some automatic welding processes. In pulsed current welding there are two current levels. the high current and low current.

10-3. WELDING WITH CONSTANT VOLTAGE
.

a. For example. the electrode melts off slower. the small light bulb will draw less than 0. The electric power delivered to homes and available at every receptacle has a constant voltage. The same voltage is maintained continuously at each outlet whether a small light bulb. or a heavy-duty electric heater with a high wattage rating. The CV electrical system is the basis of operation of the entire commercial electric power system. c. it will never rise to as high an open-circuit voltage as a constant current (CC) machine. The circuit consists of a pure resistance load which is varied from the minimum or no load to the maximum or short circuit. and as the load increases. however. at least in the upper portion of the curve. is connected. with a very low wattage rating. It has a relatively flat volt-ampere characteristic curve. This is one reason that the constant voltage (CV) machine is not used for manual shielded metal arc welding with covered electrodes. With low current. This relationship is definite and fixed. as is done when using a constant current power source. but some variations can occur. It is only used for continuous electrode wire welding. Instead of regulating the electrode wire feed rate to maintain the constant arc length. The static output characteristic curve produced by both the CV and CC machine is shown by figure 10-1 above. but the current flowing through each appliance depends on its resistance or electrical load.01 amperes of current while the electric heater may draw over 10 amperes. the electrode wire is fed into the arc at a fixed speed. The constant current (CC) curve shows that the machine produces maximum output voltage with no load. Similar curves are available for all sizes of electrode wires of different compositions and in different shielding atmospheres.The second type of power source is the constant voltage (CV) machine or the constant potential (CP) machine. the output voltage decreases. The constant voltage (CV) characteristic curve is essentially flat but with a slight droop. This relationship between melt-off rate and welding current applies to all of the arc welding processes that use a continuously fed electrode. the atmosphere that surrounds the arc. Figure 10-7 shows the melt-off rate curves for different sizes of steel electrode wires in a C02 atmosphere. The characteristic curve of a welding machine is obtained by measuring and plotting the output voltage and the output current while statically loading the machine.
. The power source is designed to provide the necessary current to melt off the electrode wire at this same rate. The current that flows through each of these circuits will be different based on the resistance of the particular item or appliance in accordance with Ohm’s law. The same principle is utilized by the CV welding system. The voltage throughout the system remains constant. the electrode is melted off more rapidly. the metal composition. This relationship is the basis of the simplified control for wire feeding using constant voltage. and welding current. This is a physical relationship that depends upon the size of the electrode. The no-load or open-circuit voltage is usually about 80 volts. When a higher current is used when welding. This concept prompted the development of the constant voltage welding power source. b. The curve may be adjusted up and down to change the voltage. Note that these curves are nearly linear.

It has characteristics similar to a standard commercial electric power generator. These voltage drops add up to the output voltage of the welding machine. and in the electrode length beyond the current pickup tip. The volt-ampere characteristics of the constant voltage power source shown by figure 10-8. This ensures a self-regulating voltage power source.d. was designed to produce substantially the same voltage at no load and at rated or full load. and maintains essentially the same voltage across the output terminals. Resistances or voltage drops occur in the welding arc and in the welding cables and connectors.
e. If the load in the circuit changes. and represent the electrical
. in the welding gun. the power source automatically adjusts its current output to satisfy this requirement.

The other voltage drops in the welding cables and connections are relatively small and constant. The arc length is controlled by setting the voltage on the power source. When the resistance of any component in the external circuit changes. A small change in arc volts results in a relatively large change in welding current. A curve having a medium slope of 2 to 3 volts per hundred amperes is preferred for CO2 gas shielded metal arc welding and for small flux-cored electrode wires. and for flux-cored arc welding with larger-diameter electrode wires. The CV welding power source provides the proper current so that the malt-off is equal to the wire feed rate. Movement of the cable assembly often changes the drag or feed rate of the electrode wire. the voltage balance will be achieved by changing the welding current in the system. A curve having a slope of 1-1/2 to 2 volts per hundred amperes is best for gas metal arc welding with nonferrous electrodes in inert gas. Most constant voltage power sources have taps or a means of adjusting the slope of the voltampere curve.resistance load on the welding power source. The constant voltage power source is continually changing its current output in order to maintain the voltage drop in the external portion of the welding circuit. The CV power source and fixed wire feed speed system is self-regulating. Figure 10-9 shows that if the arc length shortens slightly. the welding current increases by approximately 100 amperes. The characteristics of the welding power source must be designed to provide a stable arc when gas metal arc welding with different electrode sizes and metals and in different atmospheres. The volt-age drop across the welding arc is directly dependent upon the arc length. A steeper slope of 3 to 4 volts per hundred amperes is recommended
. g. for submerged arc welding. The greatest voltage drop occurs across the welding arc. This change in arc length greatly increases the melt-off rate and quickly brings the arc length back to normal. The same corrective action occurs if the wire feeder has a temporary reduction in speed.
f. Changes in wire feed speed which might occur when the welder moves the gun toward or away from the work are compensated for by changing the current and the melt-off rate briefly until equilibrium is reestablished. The welding current is controlled by adjusting the wire feed speed.

The dynamic characteristics of the power source must be carefully engineered. In most machines. a different amount of inductance is included in the circuit for the different slopes. The current density (amperes/sq in. The flatter the curve.) relationship for different electrode wire sizes and different currents is shown by figure 10-11.
h.for short circuiting arc transfer.
. There is a vast difference between the current density employed for gas metal arc welding with a fine electrode wire compared with conventional shielded metal arc welding with a covered electrode. Refer again to figure 10-9. These three slopes are shown in figure 10-10. The constant voltage welding power system has its greatest advantage when the current density of the electrode wire is high. i. If the voltage changes abruptly with a short circuit. This is an advantage in starting the arc but will create unwanted spatter if not controlled. the current will tend to increase quickly to a very high value. It is controlled by adding reactance or inductance in the circuit. the more the current changes for an equal change in arc voltage. This changes the time factor or response time and provides for a stable arc.

The electrical arc welding circuit is the same as any electrical circuit. l. k. or the flow of electricity. The constant voltage power system should not be used for shielded metal-arc welding. It may overload and damage the power source by drawing too much current too long. or the force required to cause the current to flow.j. General.
. In the simplest electrical circuits. Direct current electrode negative (DCEN) can be used for submerged arc welding and flux-cored arc welding. and resistance. pressure. Direct current electrode positive (DCEP) is used for gas metal arc welding. DC STRAIGHT AND REVERSE POLARITY WELDING a. or the force required to regulate the flow of current. there are three factors: current. 10-4. When dc electrode negative (DCEN) is used. Constant voltage welding with alternating current is normally not used. It can be used for carbon arc cutting and gouging with small electrodes and the arc welding processes. the arc is erratic and produces an inferior weld. It can be used for submerged arc welding and for electroslag welding.

The difference of potential or voltage causes current to flow in an electrical circuit. Every component in the circuit. It is designated by the letter R. The letter E is used to designate voltage or EMF. and an ammeter. Outside of a device that sets up the EMF. The longer line of the symbol represents the positive terminal. (3) Resistance is the restriction to current flow in an electrical circuit. The resistance in the circuit is shown by a zigzag symbol. including the conductor. b. An ohmmeter must never be used to measure resistance in a circuit when current is flowing. The unit of electrical resistance is the ohm. This force or potential is called electromotive force or EMF. The voltmeter is a high resistance meter shown by the round circle and arrow adjacent to the letter E. The current will flow from the negative terminal through the resistance of the arc to the positive terminal. The measure of electrical pressure is the volt. Current flows easier through some conductors than others. that is. and the temperature of the conductor. has some resistance to current flow. It also shows a symbol for a battery. Replace the battery with a welding generator. the cross-sectional area. Electrical circuits.
c. The voltage between two points in an electrical circuit is called the difference in potential. The pressure or voltage across the battery can be measured by a voltmeter. The arc welding circuit is shown by figure 10-13. since they are both a source of EMF (or voltage). The letter I is used to designate current amperes. such as a generator or a battery. A few changes to the circuit shown by figure 10-12.(1) Current is a rate of flow and is measured by the amount of electricity that flows through a wire in one second. A simple electrical circuit is shown by figure 10-12. The term ampere denotes the amount of current per second that flows in a circuit. The ammeter is a low resistance meter shown by the round circle and arrow adjacent to the letter I. and replace the resistor with a welding arc which is also a resistance to current flow. the current flows from the negative (-) to the positive (+). The resistance of a resistor can be measured by an ohmmeter. (2) Pressure is the force that causes a current to flow. above. the resistance of some conductors is less than others. Resistance depends on the material. The arrow shows the direction of current flow.
. Arc Welding Circuit. can be made to represent an arc welding circuit. This circuit includes two meters for electrical measurement: a voltmeter.

Before the arc is struck or if the arc is broken. which is a combination of an ammeter and a voltmeter. or kilowatt hours.d. The early coated electrodes for welding steel gave best results with the electrode positive or reverse polarity. Thus. The voltmeter shown in figure 10-12 will measure the welding machine output and the voltage across the arc. the polarity of the welding current was termed straight. it is necessary to know the amount of work involved. it was necessary to remove the cables from the machine terminals and replace them in the reverse position. and is higher than the arc voltage or voltage across the machine when current is flowing. and is measured in watts. In order to change the polarity of the welding current. Another unit in an electrical circuit is the unit of power. and is expressed as watt seconds. When welding with the electrode negative. In the early days of arc welding. When conditions such as welding cast iron or nonferrous metals made it advisable to minimize the heat in the base metal. bare electrodes were still used. 10-5. very low resistance conductor. it was normal to connect the positive side of the generator to the work and the negative side to the electrode. In addition to power. which are essentially the same. The shunt is a calibrated. The ammeter used in a welding circuit is a millivoltmeter calibrated in amperes connected across a high current shunt in the welding circuit. and reverse when the electrode was positive. It was necessary to change polarity frequently when using both bare and covered electrodes. Power in circuit is the product of the current in amperes multiplied by the pressure in volts. This provided 65 to 75 percent of the heat to the work side of the circuit to increase penetration. Power is measured by a wattmeter. WELDING ARCS
. Welding machines were equipped with switches that changed the polarity of the terminals and with dual reading meters. This is known as the open circuit voltage. g. however. Reverse and Straight Polarity. e. In marking welding machines and polarity switches. electrode negative (DCEN) is the same as straight polarity (dcsp). joules. and electrode positive (DCEP) is the same as reverse polarity (dcrp). when welding was done with bare metal electrodes on steel. f. these old terms were used and indicated the polarity as straight when the electrode was negative. and the welding current polarity was said to be reverse. The rate of producing or using energy is called power. the work was made negative and the electrode positive. the voltmeter will read the voltage across the machine with no current flowing in the circuit. The welder could quickly change the polarity of the welding current. Electrical work or energy is the product of power multiplied by time.

Types of Welding Arcs. One uses the nonconsumable electrode and the other uses the consumable electrode. the arc is restricted at the electrode and spreads out toward the workpiece. If a higher current is used. and plasma arc welding.000° Kelvin. in a special case. This means that there is a certain current necessary to sustain an arc of different lengths. This is because
. The plasma carries most of the current. (2) A welding arc is a sustained electrical discharge through a high conducting plasma. Whether the electrode is positive or negative. The arc is used as a concentrated source of high temperature heat that can be moved and manipulated to melt the base metal and filler metal to produce welds. gas metal arc welding. (3) The length of the arc is proportional to the voltage across the arc. The welding processes that use the nonconsumable electrode arc are carbon arc welding. noise. b. gas tungsten arc welding. The welding arc is a steady-state condition maintained at the gap between an electrode and workpiece that can carry current ranging from as low as 5 amperes to as high as 2000 amperes and a voltage as low as 10 volts to the highest voltages used on large plasma units. the point being the arcing end of the electrode and the plane being the arcing area of the workpiece. shown by figure 10-14. takes on a nonlinear form which in one area has a negative slope. (1) The main function of the arc is to produce heat. The welding arc is somewhat different from other electrical arcs since it has a point-to-plane geometric configuration. General. (1) The nonconsumable electrode does not melt in the arc and filler metal is not carried across the arc stream. The temperature and the diameter of the central plasma depend on the amount of current passing through the arc. Function of the Welding Arc. bombardment that removes surface films from the base metal. and the electrode size and type. If the arc length is increased beyond a certain point. (5) The curve of an arc. At the same time. the shielding atmosphere.a. The welding processes that use the consumable electrode arc are shielded metal arc welding. and. The outer flame of the arc is much cooler and tends to keep the plasma in the center. The arc voltage increases slightly as the current increases. c. This is true except for the very low-current arc which has a higher arc voltage. a longer arc can be maintained. (2) The consumable electrode melts in the arc and is carried across the arc in a stream to become the deposited filler metal. It produces sufficient thermal energy which is useful for joining metals by fusion. the arc will suddenly go out. (4) The arc column is normally round in cross section and is made up of an inner core of plasma and an outer flame. The plasma of a highcurrent arc can reach a temperature of 5000 to 50. flux-cored arc welding. There are two basic types of welding arcs. it produces a bright light. and submerged arc welding.

The emitted electrons are attracted to the positive pole. and raise the temperature of the argon shielding gas atoms by colliding with them. where they are absorbed.the low-current plasma has a fairly small cross-sectional area. On the left. This heat keeps the tungsten electrode hot enough for electron emission. The positively charged gaseous atoms are attracted to the negative electrode where their kinetic (motion) energy is converted to heat. Positive ions also cross the arc. Positive ions are much heavier than the electrons. They travel from the positive pole. or the electrode. When the arc is started.
. the tungsten arc is connected for direct current electrode negative (DCEN). and as the current increases the cross section of the plasma increases and the resistance is reduced.
(6) The arc is maintained when electrons are emitted or evaporated from the surface of the negative pole (cathode) and flow across a region of hot electrically charged gas to the positive pole (anode). The collisions of electrons with atoms and molecules produce thermal ionization of some of the atoms of the shielding gas. to the negative pole. or the work. approximately 99 percent. Emission of electrons from the surface of the tungsten cathode is known as thermionic emission. the electrode becomes hot and emits electrons. travel through the arc gap. but help carry the current flow of the relatively low voltage welding arc. The electrons colliding with the work create the intense localized heat which provides melting and deep penetration of the base metals. (7) Arc action can best be explained by considering the dc tungsten electrode arc in an inert gas atmosphere as shown by figure 10-15. The continuous feeding of electrons into the welding circuit from the power source accounts for the continuing balance between electrons and ions in the arc. The conductivity of the arc increases at a greater rate than simple proportionality to current. is via electron flow rather than through the flow of positive ions. Cathode and anode are electrical terms for the negative and positive poles. The largest portion of the current flow.

This appears as an etched surface and is known as catholic etching. as shown by figure 10-15. This plasma is used for welding. A larger electrode with more heat-absorbing capacity is used for DCEP (dcsp) than for DCEN (dcrp) for the same welding current. the cooling effect of the electrode and the work causes a rapid drop in potential. These two regions are known as the anode and cathode drop. One result of DCEP welding is the cleaning effect on the base metal adjacent to the arc area. since less heat is generated at the work. At the end regions. the penetration is not so great. it requires a higher voltage. (9) Constriction occurs in a plasma arc torch by making the arc pass through a small hole in a water-cooled copper nozzle. high temperature gas jet or plasma emerges. the electrons flow from the work to the electrode where they create intense heat. the maximum heat occurs at the positive pole (anode). By flowing additional gas through the small hole.(8) In the dc tungsten to base metal arc in an inert gas atmosphere. cutting. In addition. This positive ion bombardment also occurs during the reverse polarity half-cycle when using alternating current for welding. and metal spraying. It is a characteristic of the arc that the more it is cooled the hotter it gets. and a region adjacent to the work. the arc is further constricted and a high velocity. according
. It results from positive ion bombardment. a region adjacent to the electrode. (10) The arc length or gap between the electrode and the work can be divided into three regions: a central region. The electrode tends to overheat. however. When the electrode is positive (anode) and the work is negative (cathode).

produces a plasma jet. or the workpiece.
(11) The cathode drop is the electrical connection between the arc column and the negative pole (cathode). In the carbon arc. The arc
. The reduction in temperature occurs because there are fewer ions in this region. or the electrode. This field. There is a relatively large temperature and potential drop at this point. in turn. In the central region. a stable dc arc is obtained when the carbon is negative. and are therefore used for welding electrodes. In this condition. tends to constrict the plasma and is known as the magnetic pinch effect. The electrons are emitted by the cathode and given to the arc column at this point. which is considerably lower. since both are good emitters of electrons. the electrode is melted and molten metal is carried across the arc. (12) The anode drop occurs at the other end of the arc and is the electrical connection between the positive pole (anode) and the arc column. Tungsten and carbon provide thermic emissions. Consumable Electrode Arc. The constriction causes high pressures in the arc plasma and extremely high velocities. a circular magnetic field surrounds the arc. Since tungsten has the highest melting point of any metal. and about 2/3 of the heat occurs at the positive pole (anode). about 1/3 of the heat occurs at the negative pole (cathode). The stability of an arc depends on the smoothness of the flow of electrons at this point. This. Figure 10-16 shows the distribution of heat in the arc. They have high melting temperatures. The heat liberated at the anode and at the cathode is greater than that from the arc column.to the direction of current flow. The speed of the plasma jet approaches sonic speed. it is preferred. which varies in these three regions. Carbon Arc. d. A uniform arc length is maintained between the electrode and the base metal by feeding the electrode into the arc as fast as it melts. produced by the current flow. e. The temperature changes from that of the arc column to that of the anode. In the consumable electrode welding arc. The length of the central region or arc column represents 99 percent of the arc length and is linear with respect to arc voltage. are practically nonconsumable.

the electrode size. (a) Surface tension of a liquid causes the surface of the liquid to contract to the smallest possible area. Penetration is minimum. which provides deep penetration. When coated electrodes are operated on ac. Consumable Electrode Arc. the plasma jet. the electrode is the negative pole (DCEN) and the melt-off rate is high. This is shown by figure 10-17. When straight polarity welding with an E6012 electrode. and the electrode composition. The type of metal transfer dictates the usefulness of the welding process. With a bare steel electrode on steel. but this is now the base metal. the polarity of the electrode. and electromagnetic force. The type of transfer depends on the current density. When reverse polarity welding with an E6010 electrode (DCEP). the stability of the welding pool.atmosphere has a great effect on the polarity of maximum heat. Usually the maximum heat occurs at the negative pole (cathode). to droplets larger in diameter than the electrode. The metal being transferred ranges from small droplets.
f. Bare electrodes are operated on straight polarity (DCEN) so that maximum heat is at the base metal (anode) to ensure enough penetration. the maximum heat still occurs at the negative pole (cathode). the same amount of heat is produced on each polarity of the arc. This tension tends to hold the liquid drops on the end of a
. In shielded metal arc welding. the arc atmosphere. (2) Several forces affect the transfer of liquid metal across an arc. These are surface tension. gravity in flat position welding. smaller than the diameter of the electrode. It affects the welding position that can be used. and the amount of spatter loss. the arc atmosphere depends on the composition of the coating on the electrode. (1) The forces that cause metal to transfer across the arc are similar for all the consumable electrode arc welding processes. the depth of weld penetration. the surface contour of the weld. the polarity of maximum heat is the positive pole (anode).

The electromagnetic force acts on the liquid metal drop when it is about to detach from the electrode. Molten metal drops in the process of detachment from the end of the electrode. When the welding current flows through the electrode. This force works against the transfer of metal across the arc and helps keep molten metal in the weld pool when welding in the overhead position.melting electrode without regard to welding position. The drop that has started to separate will be given a push which increases the rate of separation. the magnetic force acts away from the point of constriction in both directions. the magnetic force tends to detach the drop. (c) Earth gravity detaches the liquid drop when the electrode is pointed downward and is a restraining force when the electrode is pointing upward. at the end of the electrode. The maximum pressure is radial to the axis of the electrode and at high currents causes the drop to lengthen. The current density and the arc temperature are the highest where the arc is most constricted. It gives the drop stiffness and causes it to project in line with the electrode regardless of the welding position. are accelerated towards the work piece by the plasma jet. Magnetic force also sets up a pressure within the liquid drop. There are two ways in which the electromagnetic force acts to detach a drop at the tip of the electrode. or in flight. The difference between the mass of the molten metal droplet and the mass of the workpiece has a gravitational effect which tends to pull the droplet to the workpiece. The electromagnetic force depends upon whether the cross section is increasing or decreasing. Figure 10-18 illustrates these two points. a magnetic field is set up around it. An arc operating in a gaseous atmosphere contains a plasma jet which flows along the center of the arc column between the electrode and the base metal. As the metal melts.
. (b) The welding arc is constricted at the electrode and spreads or flares out at the workpiece. When there is a constriction or necking down which occurs when the drop is about to detach. When a drop is larger in diameter than the electrode and the electrode is positive (DCEP). An arc between two electrodes will not deposit metal on either. the cross-sectional area of the electrode changes at the molten tip. Gravity has a noticeable effect only at low currents. (d) Electromagnetic force also helps transfer metal across the arc.

The maximum value in one direction is reached at the 90° position.10-6. AC WELDING a. General. When the current rises from zero to a maximum. Figure 10-19 is a graphical representation of a cycle and is called a sine wave.
. and finally returns to zero again. returns to zero. it is said to have completed one cycle. It is generated by one revolution of a single loop coil armature in a two-pole alternating current generator. Alternating current is an electrical current which flows back and forth at regular intervals in a circuit. increases to a maximum in the opposite direction. and in the other direction at the 270° position. (1) A cycle is divided into 360 degrees.

the arc is extinguished during each half-cycle as the current reduces to zero. The greater the arc length. The sine wave is the simplest form of alternating current. There are two variations of electrical power conversion. After reignition. d. unless otherwise marked. This causes rectification to a lesser or greater degree. All ac meters. Complete rectification has been
. measured in hertz. (1) In the first variation. f. e. With an alternating flow of current. g. an ac ammeter will measure a value. but it is followed by a rectifier which changes alternating current to direct current for dc welding.(2) The number of times this cycle is repeated in one second is called the frequency. read effective values of current and voltage. As the current decreases again. The effective direct current value of an alternating current or voltage is the product of 0. anode. but an alternating current is not a steady current. An alternating current is said to be equivalent to a direct current when it produces the same average heating effect under exactly similar conditions. or rootmean-square (RMS) voltage. The voltage and current in the ac welding arc follow the sine wave and return to zero twice each cycle. the less the arc gas will be heated by the hot electrode terminals. c. It is either generated at the point of use or converted from available power from the utility line. requiring reignition as the voltage rises again. the cathode emitter may cool enough during the fall of the current to zero to stop the arc completely. a transformer converts the relatively high voltages from the utility line to a liner voltage for ac welding. An ac voltmeter measures the value of both the positive and negative parts of the sine wave. An alternating current has no unit of its own. b. the current will flow by different amounts during each half-cycle.707 multiplied by the maximum value. (2) The second variation is similar in that it includes the transformer to lower the voltage. through the usual falling volts-amperes characteristic. This is used since the heating effect of a negative current is the same as that of a positive current. When the electrode and welding work have different thermal inertia ability to emit electrons. and a higher reignition potential will be required. with increasing current. called the effective value. Depending upon the thermal inertia of the hot electrode terminals and plasma. it passes. The ampere is defined as a steady rate of flow. of an alternating current which is shown in amperes. Therefore. the ampere. the arc potential is lower because the temperature and degree of ionization of the arc path correspond to the heated condition of the plasma. The frequency is so fast that the arc appears continuous and steady. Electrical power for arc welding is obtained in two different ways. and cathode during the time of increasing current. It reads the effective. but is measured in terms of direct current. Alternating current and voltage are measured with ac meters. Alternating current for arc welding normally has the same frequency as the line current.

The smaller puddle is more easily controlled.
b. Since the area covered with each pass is small. This procedure enables the welder to obtain complete joint penetration without excessive penetration and overheating while the first few passes are being deposited. Multiple layer welding is used when maximum ductility of a steel weld is desired or several layers are required in welding thick metal. MULTILAYER WELDING a. c. 10-7. and therefore improved in ductility. the weld puddle is reduced in size. and the welder can avoid oxides. and incomplete fusion with the base metal. This method permits the metal deposited in a given layer to be partly or wholly refined by the succeeding layers. Multiple layer welding is accomplished by depositing filler metal in successive passes along the joint until it is filled (fig. 10-20). The multilayer method allows the welder to concentrate on getting good penetration at the root of the V in the first pass or layer. after
. The final layer is easily controlled to obtain a good smooth surface.experienced in arcs with a hot tungsten electrode and a cold copper opposing terminal. slag inclusions. The lower layer of weld metal. Partial rectification of one half-cycle is common when using the TIG welding process with ac power.

This is the most widely used method for general welding applications. In work where this added quality is desired in the top layer of the welded joint. Thus. In effect. the weld area is being heat treated. Advantages. an excess of weld metal is deposited on the finished weld and then machined off. Disadvantages. d. manual metal-arc.
c. ARC PROCESSES
10-8. Slag removal. horizontal. heat-treatable steels. SMAW lends itself very well to field work (fig. which may have to be removed. The purpose of this last layer is simply to provide welding heat to refine layer of weld metal. These include low-carbon or mild steels.
. (1) The core of the covered electrode consists of either a solid metal rod of drawn or cast material. or one fabricated by encasing metal powders in a metallic sheath. and high-alloy steels such as stainless steels. The core rod conducts the electric current to the arc and provides filler metal for the joint. Processes. vertical. The SMAW process can be used for welding most structural and alloy steels. SHIELDED METAL-ARC WELDING (SMAW) a.
Section II. b. or stick-electrode welding. and spatter add to the cost of SMAW. It is an arc welding process in which the joining of metals is produced by heat from an electric arc that is maintained between the tip of a covered electrode and the base metal surface of the joint being welded. is reheated by the upper layer and then cooled again. 10-21). SMAW is used for joining common nickel alloys and can be used for copper and aluminum alloys. This welding process can be used in all positions--flat. Unused electrode stubs and spatter account for about 44 percent of the consumed electrodes. General. Another cost is the entrapment of slag in the form of inclusions. unused electrode stubs.cooling. The electrode covering shields the molten metal from the atmosphere as it is transferred across the arc and improves the smoothness or stability of the arc. It is also refereed to as metallic arc. low-alloy. or overhead--and requires only the simplest equipment.

The other is attached to the electrode holder. gas expansion. melting takes place almost instantaneously as the arc contacts the metal. the surface tension is unable to retain much molten metal and slag in the crater. The shielding ingredients vary according to the type of electrode. chemical composition.
. The shielding and other ingredients in the covering and core wire control the mechanical properties.
(4) Welding begins when an electric arc is struck between the tip of the electrode and the work. melting and fusing a portion of the base metal and adding filler metal as the arc progresses. and metallurgical structure of the weld metal. as shown in figure 10-22. See figure 10-23. the work. Therefore. For welds in other positions. The intense heat of the arc melts the tip of the electrode and the surface of the work beneath the arc. and surface tension.(2) Arc shielding is obtained from gases which form as a result of the decomposition of certain ingredients in the covering. filler metal is deposited as the electrode is progressively consumed. If welds are made in either the flat or the horizontal position. an electrode holder. electric and electromagnetic forces. One of the two cables from the power source is attached to the work. This circuit begins with the electric power source and includes the welding cables. (3) Shielded metal arc welding employs the heat of the arc to melt the base metal and the tip of a consumable covered electrode. In other positions. and an arc welding electrode. Gravity is the principal force which accounts for the transfer of filler metal in flat position welding. smaller electrodes must be used to avoid excessive loss of weld metal and slag. Since the arc is one of the hottest of the commercial sources of heat (temperatures above 9000°F (5000°C) have been measured at its center). metal transfer is induced by the force of gravity. The arc is moved over the work at an appropriate arc length and travel speed. then transfer through the arc stream into the molten weld pool. gravity works against the other forces. a ground clamp. The electrode and the work are part of an electric circuit known as the welding circuit. (a) Gravity. as well as arc characteristics of the electrode. Tiny globules of molten metal rapidly form on the tip of the electrode. In this manner.

straight-polarity.(b) Gas expansion. and travel speed are very important to the quality of the deposited SMAW bead. f. mineralcoated electrodes. (d) Electrical forces. cables. and overhead position welding. as is the molten metal globule at the tip. wire brush. (1) Welding voltage. The force which keeps the filler metal and slag globules in contact with molten base or weld metal in the crater is known as surface tension. and to determine the shape of weld contours. e. Therefore. (c) Electromagnetic forces. vertical. Manual welding equipment includes a power source (transformer. Welding Parameters. chipping hammer. electrode holder. and electrodes. Figures 10-24 thru 10-30 show the travel speed limits for the electrodes listed in table 10-1 below. The coating extending beyond the metal tip of the electrode controls the direction of the rapid gas expansion and directs the molten metal globule into the weld metal pool formed in the base metal. The equipment needed for shielded metal-arc welding is much less complex than that needed for other arc welding processes. regardless of the position of welding. which do not produce large volumes of gas. dc generator. This force is especially helpful when using direct-current. Gases are produced by the burning and volatilization of the electrode coating. The force produced by the voltage across the arc pulls the small.
. current. connectors. or dc rectifier). Equipment. It helps to retain the molten metal in horizontal. (e) Surface tension. The electrode tip is an electrical conductor. These forces produce a pinching effect on the metal globules and speed up the separation of the molten metal from the end of the electrode. the globule is affected by magnetic forces acting at 90 degrees to the direction of the current flow. and overhead welding. and are expanded by the heat of the boiling electrode tip. pinched-off globule of metal. This is particularly helpful in transferring metal in horizontal. vertical. Table 10-1 shows voltage limits for some SMAW electrodes.

.

(2) The process requires sufficient electric current to melt both the electrode and a proper amount of base metal, and an appropriate gap between the tip of the electrode and base metal or molten weld pool. These requirements are necessary for coalescence. The sizes and types of electrodes for shielded metal arc welding define the arc voltage requirements (within the overall range of 16 to 40 V) and the amperage requirements (within the overall range of 20 to 550 A). The current may be either alternating or direct, but the power source must be able to control the current level in order to respond to the complex variables of the welding process itself.

g. Covered Electrodes. In addition to establishing the arc and supplying filler metal for the weld deposit, the electrode introduces other materials into or around the arc. Depending upon the type of electrode being used, the covering performs one or more of the following functions: (1) Provides a gas to shield the arc and prevent excessive atmospheric contamination of the molten filler metal as it travels across the arc. (2) Provides scavengers, deoxidizers, and fluxing agents to cleanse the weld and prevent excessive grain growth in the weld metal. (3) Establishes the electrical characteristics of the electrode. (4) Provides a slag blanket to protect the hot weld metal from the air and enhance the mechanical properties, bead shape, and surface cleanliness of the weld metal. (5) Provides a means of adding alloying elements to change the mechanical properties of the weld metal. Functions 1 and 4 prevent the pick-up of oxygen and nitrogen from the air by the molten filler metal in the arc stream and by the weld metal as it solidifies and cools. The covering on shielded metal arc electrodes is applied by either the extrusion or the dipping process. Extrusion is much more widely used. The dipping process is used primarily for cast and some fabricated core rods. In either case, the covering contains most of the shielding, scavenging, and deoxidizing materials. Most SMAW electrodes have a solid metal core. Some are made with a fabricated or composite core consisting of metal powders encased in a metallic sheath. In this latter case, the purpose of some or even all of the metal powders is to produce an alloy weld deposit. In addition to improving the mechanical properties of the weld metal, the covering on the electrode can be designed for welding with alternating current. With ac, the welding arc goes out and is reestablished each time the current reverses its direction. For good arc stability, it is necessary to have a gas in the arc stream that will remain ionized during each reversal of the current. This ionized gas makes possible the reignition of the arc. Gases that readily ionize are available from a variety of compounds, including those that contain potassium. It is the incorporation of these compounds in the electrode covering that enables the electrode to operate on ac. To increase the deposition rate, the coverings of some carbon and low alloy steel electrodes contain iron powder. The iron powder is another source of metal available for deposition, in addition to that obtained from the core of the electrode. The presence of iron powder in the covering also makes more efficient use of the arc energy. Metal powders other than iron are frequently used to alter the mechanical properties of the weld metal. The thick coverings on electrodes with relatively large amounts of iron powder increase the depth of the crucible at the tip of the electrode. This deep crucible helps contain the heat of the

arc and maintains a constant arc length by using the "drag" technique. When iron or other metal powders are added in relatively large amounts, the deposition rate and welding speed usually increase. Iron powder electrodes with thick coverings reduce the level of skill needed to weld. The tip of the electrode can be dragged along the surface of the work while maintaining a welding arc. For this reason, heavy iron powder electrodes frequently are called "drag electrodes." Deposition rates are high; but because slag solidification is slow, these electrodes are not suitable for out-of-position use. h. Electrode Classification System. The SMAW electrode classification code contains an E and three numbers, followed by a dash and either "15" or "16" (EXXX15). The E designates that the material is an electrode and the three digits indicate composition. Sometimes there are letters following the three digits; these letters indicate a modification of the standard composition. The "15" or "16" specifies the type of current with which these electrodes may be used. Both designations indicate that the electrode is usable in all positions: flat, horizontal, vertical and overhead. (1) The "15" indicates that the covering of this electrode is a lime type, which contains a large proportion of calcium or alkaline earth materials. These electrodes are usable with dc reverse-polarity only. (2) The designation "16" indicates electrodes that have a lime-or titania-type covering with a large proportion of titanium-bearing minerals. The coverings of these electrodes also contain readily ionizing elements, such as potassium, to stabilize the arc for ac welding. i. Chemical Requirements. The AWS divides SMAW electrodes into two groups: mild steel and low-alloy steel. The E60XX and E70XX electrodes are in the mild steel specification. The chemical requirements for E70XX electrodes are listed in AWS A5.1 and allow for wide variations of composition of the deposited weld metal. There are no specified chemical requirements for the E60XX electrodes. The low-alloy specification contains electrode classifications E70XX through E120XX. These codes have a suffix indicating the chemical requirements of the class of electrodes (e. g., E7010-A1 or E8018-C1). The composition of lowalloy E70XX electrodes is controlled much more closely than that of mild steel E70XX electrodes. Low-alloy electrodes of the low-hydrogen classification (EXX15, EXX16, EXX18) require special handling to keep the coatings from picking up water. Manufacturers’ recommendations about storage and rebaking must be followed for these electrodes. AWS A5.5 provides a specific listing of chemical requirements. j. Weld Metal Mechanical Properties. The AWS requires the deposited weld metal to have a minimum tensile strength of 60,000 to 100,000 psi (413,700 to 689,500 kPa), with minimum elongations of 20 to 35 percent. k. Arc Shielding. (1) The arc shielding action, illustrated in figure 10-31, is essentially the same for the different types of electrodes, but the specific method of shielding and the volume of slag

produced vary from type to type. The bulk of the covering materials in some electrodes is converted to gas by the heat of the arc, and only a small amount of slag is produced. This type of electrode depends largely upon a gaseous shield to prevent atmospheric contamination. Weld metal from such electrodes can be identified by the incomplete or light layer of slag which covers the bead.

(2) For electrodes at the other extreme, the bulk of the covering is converted to slag by the arc heat, and only a small volume of shielding gas is produced. The tiny globules of metal transferred across the arc are entirely coated with a thin film of molten slag. This slag floats to the weld puddle surface because it is lighter than the metal. It solidifies after the weld metal has solidified. Welds made with these electrodes are identified by the heavy slag deposits that completely cover the weld beads. Between these extremes is a wide variety of electrode types, each with a different combination of gas and slag shielding. (3) The variations in the amount of slag and gas shielding also influence the welding characteristics of the different types of covered electrodes. Electrodes that have a heavy slag carry high amperage and have high deposition rates. These electrodes are ideal for making large beads in the flat position. Electrodes that develop a gaseous arc shield and have a light layer of slag carry lower amperage and have lower deposition rates. These electrodes produce a smaller weld pool and are better suited for making welds in the vertical and overhead positions. Because of the differences in their welding characteristics, one type of covered electrode will usually be best suited for a given application. 10-9. GAS TUNGSTEN ARC (TIG) WELDING (GTAW) a. General. Gas tungsten arc welding (TIG welding or GTAW) is a process in which the joining of metals is produced by heating therewith an arc between a tungsten (nonconsumable) electrode and the work. A shielding gas is used, normally argon. TIG welding is normally done with a pure tungsten or tungsten alloy rod, but multiple electrodes are sometimes used. The heated weld zone, molten metal, and tungsten electrode are shielded from the atmosphere by a covering of inert gas fed through the electrode holder. Filler metal may or may not be added. A weld is made

by applying the arc so that the touching workpiece and filler metal are melted and joined as the weld metal solidifies. This process is similar to other arc welding processes in that the heat is generated by an arc between a nonconsumable electrode and the workpiece, but the equipment and electrode type distinguish TIG from other arc welding processes. See figure 10-32.

b. Equipment. The basic features of the equipment used in TIG welding are shown in figure 1033. The major components required for TIG welding are:

(1) the welding machine, or power source (2) the welding electrode holder and the tungsten electrode (3) the shielding gas supply and controls (4) Several optional accessories are available, which include a foot rheostat to control the current while welding, water circulating systems to cool the electrode holders, and arc timers. NOTE There are ac and dc power units with built-in high frequency generators designed specifically for TIG welding. These automatically control gas and water flow when welding begins and ends. If the electrode holder (torch) is water-cooled, a supply of cooling water is necessary. Electrode holders are made so that electrodes and gas nozzles can readily be changed. Mechanized TIG welding equipment may include devices for checking and adjusting the welding torch level, equipment for work handling, provisions for initiating the arc and controlling gas and water flow, and filler metal feed mechanisms. c. Advantages. Gas tungsten arc welding is the most popular method for welding aluminum stainless steels, and nickel-base alloys. It produces top quality welds in almost all metals and alloys used by industry. The process provides more precise control of the weld than any other arc welding process, because the arc heat and filler metal are independently controlled. Visibility is excellent because no smoke or fumes are produced during welding, and there is no slag or spatter that must be cleaned between passes or on a completed weld. TIG welding also has reduced distortion in the weld joint because of the concentrated heat source. The gas tungsten arc welding process is very good for joining thin base metals because of excellent control of heat input. As in

oxyacetylene welding, the heat source and the addition of filler metal can be separately controlled. Because the electrode is nonconsumable, the process can be used to weld by fusion alone without the addition of filler metal. It can be used on almost all metals, but it is generally not used for the very low melting metals such as solders, or lead, tin, or zinc alloys. It is especially useful for joining aluminum and magnesium which form refractory oxides, and also for the reactive metals like titanium and zirconium, which dissolve oxygen and nitrogen and become embrittled if exposed to air while melting. In very critical service applications or for very expensive metals or parts, the materials should be carefully cleaned of surface dirt, grease, and oxides before welding. d. Disadvantages. TIG welding is expensive because the arc travel speed and weld metal deposition rates are lower than with some other methods. Some limitations of the gas tungsten arc process are: (1) The process is slower than consumable electrode arc welding processes. (2) Transfer of molten tungsten from the electrode to the weld causes contamination. The resulting tungsten inclusion is hard and brittle. (3) Exposure of the hot filler rod to air using improper welding techniques causes weld metal contamination. (4) Inert gases for shielding and tungsten electrode costs add to the total cost of welding compared to other processes. Argon and helium used for shielding the arc are relatively expensive. (5) Equipment costs are greater than that for other processes, such as shielded metal arc welding, which require less precise controls. For these reasons, the gas tungsten arc welding process is generally not commercially competitive with other processes for welding the heavier gauges of metal if they can be readily welded by the shielded metal arc, submerged arc, or gas metal arc welding processes with adequate quality. e. Process Principles. (1) Before welding begins, all oil, grease, paint, rust, dirt, and other contaminants must be removed from the welded areas. This may be accomplished by mechanical means or by the use of vapor or liquid cleaners. (2) Striking the arc may be done by any of the following methods: (a) Touching the electrode to the work momentarily and quickly withdrawing it. (b) Using an apparatus that will cause a spark to jump from the electrode to the work.

(c) Using an apparatus that initiates and maintains a small pilot arc, providing an ionized path for the main arc. (3) High frequency arc stabilizers are required when alternating current is used. They provide the type of arc starting described in (2)(b) above. High frequency arc initiation occurs when a high frequency, high voltage signal is superimposed on the welding circuit. High voltage (low current) ionizes the shielding gas between the electrode and the workpiece, which makes the gas conductive and initiates the arc. Inert gases are not conductive until ionized. For dc welding, the high frequency voltage is cut off after arc initiation. However, with ac welding, it usually remains on during welding, especially when welding aluminum. (4) When welding manually, once the arc is started, the torch is held at a travel angle of about 15 degrees. For mechanized welding, the electrode holder is positioned vertically to the surface. (5) To start manual welding, the arc is moved in a small circle until a pool of molten metal forms. The establishment and maintenance of a suitable weld pool is important and welding must not proceed ahead of the puddle. Once adequate fusion is obtained, a weld is made by gradually moving the electrode along the parts to be welded to melt the adjoining surfaces. Solidification of the molten metal follows progression of the arc along the joint, and completes the welding cycle. (6) The welding rod and torch must be moved progressively and smoothly so the weld pool, hot welding rod end, and hot solidified weld are not exposed to air that will contaminate the weld metal area or heat-affected zone. A large shielding gas cover will prevent exposure to air. Shielding gas is normally argon. (7) The welding rod is held at an angle of about 15 degrees to the work surface and slowly fed into the molten pool. During welding, the hot end of the welding rod must not be removed from the inert gas shield. A second method is to press the welding rod against the work, in line with the weld, and melt the rod along with the joint edges. This method is used often in multiple pass welding of V-groove joints. A third method, used frequently in weld surfacing and in making large welds, is to feed filler metal continuously into the molten weld pool by oscillating the welding rod and arc from side to side. The welding rod moves in one direction while the arc moves in the opposite direction, but the welding rod is at all times near the arc and feeding into the molten pool. When filler metal is required in automatic welding, the welding rod (wire) is fed mechanically through a guide into the molten weld pool. (8) The selection of welding position is determined by the mobility of the weldment, the availability of tooling and fixtures, and the welding cost. The minimum time, and therefore cost, for producing a weld is usually achieved in the flat position. Maximum joint penetration and deposition rate are obtained in this position, because a large volume of molten metal can be supported. Also, an acceptably shaped reinforcement is easily obtained in this position.

(9) Good penetration can be achieved in the vertical-up position, but the rate of welding is slower because of the effect of gravity on the molten weld metal. Penetration in vertical-down welding is poor. The molten weld metal droops, and lack of fusion occurs unless high welding speeds are used to deposit thin layers of weld metal. The welding torch is usually pointed forward at an angle of about 75 degrees from the weld surface in the vertical-up and flat positions. Too great an angle causes aspiration of air into the shielding gas and consequent oxidation of the molten weld metal. (10) Joints that may be welded by this process include all the standard types, such as square-groove and V-groove joints, T-joints, and lap joints. As a rule, it is not necessary to bevel the edges of base metal that is 1/8 in. (3.2 mm) or less in thickness. Thicker base metal is usually beveled and filler metal is always added. (11) The gas tungsten arc welding process can be used for continuous welds, intermittent welds, or for spot welds. It can be done manually or automatically by machine. (12) The major operating variables summarized briefly are: (a) Welding current, voltage, and power source characteristics. (b) Electrode composition, current carrying capacity, and shape. (c) Shielding gas--welding grade argon, helium, or mixtures of both. (d) Filler metals that are generally similar to the metal being joined and suitable for the intended service. (13) Welding is stopped by shutting off the current with foot-or-hand-controlled switches that permit the welder to start, adjust, and stop the welding current. They also allow the welder to control the welding current to obtain good fusion and penetration. Welding may also be stopped by withdrawing the electrode from the current quickly, but this can disturb the gas shielding and expose the tungsten and weld pool to oxidation. f. Filler Metals. The base metal thickness and joint design determine whether or not filler metal needs to be added to the joints. When filler metal is added during manual welding, it is applied by manually feeding the welding rod into the pool of molten metal ahead of the arc, but to one side of the center line. The technique for manual TIG welding is shown in figure 10-34.

a. General. Plasma arc welding (PAW) is a process in which coalescence, or the joining of metals, is produced by heating with a constricted arc between an electrode and the workpiece (transfer arc) or the electrode and the constricting nozzle (nontransfer arc). Shielding is obtained from the hot ionized gas issuing from the orifice, which may be supplemented by an auxiliary source of shielding gas. Shielding gas may be an inert gas or a mixture of gases. Pressure may or may not be used, and filler metal may or may not be supplied. The PAW process is shown in figure 10-35.

b. Equipment. (1) Power source. A constant current drooping characteristic power source supplying the dc welding current is recommended; however, ac/dc type power source can be used. It should have an open circuit voltage of 80 volts and have a duty cycle of 60 percent. It is desirable for the power source to have a built-in contactor and provisions for remote control current adjustment. For welding very thin metals, it should have a minimum

amperage of 2 amps. A maximum of 300 is adequate for most plasma welding applications. (2) Welding torch. The welding torch for plasma arc welding is similar in appearance to a gas tungsten arc torch, but more complex. (a) All plasma torches are water cooled, even the lowest-current range torch. This is because the arc is contained inside a chamber in the torch where it generates considerable heat. If water flow is interrupted briefly, the nozzle may melt. A cross section of a plasma arc torch head is shown by figure 10-36. During the nontransferred period, the arc will be struck between the nozzle or tip with the orifice and the tungsten electrode. Manual plasma arc torches are made in various sizes starting with 100 amps through 300 amperes. Automatic torches for machine operation are also available.

(b) The torch utilizes the 2 percent thoriated tungsten electrode similar to that used for gas tungsten welding. Since the tungsten electrode is located inside the torch, it is almost impossible to contaminate it with base metal. (3) Control console. A control console is required for plasma arc welding. The plasma arc torches are designed to connect to the control console rather than the power source. The console includes a power source for the pilot arc, delay timing systems for transferring from the pilot arc to the transferred arc, and water and gas valves and separate flow meters for the plasma gas and the shielding gas. The console is usually connected to the power source and may operate the contactor. It will also contain a high-frequency arc starting unit, a nontransferred pilot arc power supply, torch protection circuit, and an ammeter. The high-frequency generator is used to initiate the pilot arc. Torch protective

devices include water and plasma gas pressure switches which interlock with the contactor. (4) Wire feeder. A wire feeder may be used for machine or automatic welding and must be the constant speed type. The wire feeder must have a speed adjustment covering the range of from 10 in. per minute (254 mm per minute) to 125 in. per minute (3.18 m per minute) feed speed. c. Advantages and Major Uses. (1) Advantages of plasma arc welding when compared to gas tungsten arc welding stem from the fact that PAW has a higher energy concentration. Its higher temperature, constricted cross-sectional area, and the velocity of the plasma jet create a higher heat content. The other advantage is based on the stiff columnar type of arc or form of the plasma, which doesn’t flare like the gas tungsten arc. These two factors provide the following advantages: (a) The torch-to-work distance from the plasma arc is less critical than for gas tungsten arc welding. This is important for manual operation, since it gives the welder more freedom to observe and control the weld. (b) High temperature and high heat concentration of the plasma allow for the keyhole effect, which provides complete penetration single pass welding of many joints. In this operation, the heat affected zone and the form of the weld are more desirable. The heat-affected zone is smaller than with the gas tungsten arc, and the weld tends to have more parallel sides, which reduces angular distortion. (c) The higher heat concentration and the plasma jet allow for higher travel speeds. The plasma arc is more stable and is not as easily deflected to the closest point of base metal. Greater variation in joint alignment is possible with plasma arc welding. This is important when making root pass welds on pipe and other one-side weld joints. Plasma welding has deeper penetration capabilities and produces a narrower weld. This means that the depth-to-width ratio is more advantageous. (2) Uses. (a) Some of the major uses of plasma arc are its application for the manufacture of tubing. Higher production rates based on faster travel speeds result from plasma over gas tungsten arc welding. Tubing made of stainless steel, titanium, and other metals is being produced with the plasma process at higher production rates than previously with gas tungsten arc welding. (b) Most applications of plasma arc welding are in the low-current range, from 100 amperes or less. The plasma can be operated at extremely low currents to allow the welding of foil thickness material.

(c) Plasma arc welding is also used for making small welds on weldments for instrument manufacturing and other small components made of thin metal. It is used for making butt joints of wall tubing. (d) This process is also used to do work similar to electron beam welding, but with a much lower equipment cost. (3) Plasma arc welding is normally applied as a manual welding process, but is also used in automatic and machine applications. Manual application is the most popular. Semiautomatic methods of application are not useful. The normal methods of applying plasma arc welding are manual (MA), machine (ME), and automatic (AU). (4) The plasma arc welding process is an all-position welding process. Table 10-2 shows the welding position capabilities.

(5) The plasma arc welding process is able to join practically all commercially available metals. It may not be the best selection or the most economical process for welding some metals. The plasma arc welding process will join all metals that the gas tungsten arc process will weld. This is illustrated in table 10-3.

(6) Regarding thickness ranges welded by the plasma process, the keyhole mode of operation can be used only where the plasma jet can penetrate the joint. In this mode, it can be used for welding material from 1/16 in. (1.6 mm) through 1/4 in. (12.0 mm). Thickness ranges vary with different metals. The melt-in mode is used to weld material as thin as 0.002 in. (0.050 mm) up through 1/8 in. (3.2 mm). Using multipass techniques, unlimited thicknesses of metal can be welded. Note that filler rod is used for making welds in thicker material. Refer to table 10-4 for base metal thickness ranges.

d. Limitations of the Process. The major limitations of the process have to do more with the equipment and apparatus. The torch is more delicate and complex than a gas tungsten arc torch. Even the lowest rated torches must be water cooled. The tip of the tungsten and the alignment of the orifice in the nozzle is extremely important and must be maintained within very close limits.

its temperature increases because it carries the same amount of current. The water-cooling passages in the torch are relatively small and for this reason water filters and deionized water are recommended for the lower current or smaller torches. Hot ionized gases are also forced through this opening. Principles of Operation. It is used for plasma spraying or generating heat in nonmetals. (1) The plasma arc welding process is normally compared to the gas tungsten arc process.The current level of the torch cannot be exceeded without damaging the tip. The gas tungsten arc process is shown for comparison. the current flow is from the electrode inside the torch to the nozzle containing the orifice and back to the power supply.
(3) The plasma is generated by constricting the electric arc passing through the orifice of the nozzle. (b) In transferred arc mode. (a) In the non-transferred mode. The plasma has a stiff
. If an electric arc between a tungsten electrode and the work is constricted in a crosssectional area. The control console adds another piece of equipment to the system. e. The transferred arc mode is used for welding metals. (c) The difference between these two modes of operation is shown by figure 1037. This constricted arc is called a plasma. the current is transferred from the tungsten electrode inside the welding torch through the orifice to the workpiece and back to the power supply. (2) Two modes of operation are the non-transferred arc and the transferred arc. This extra equipment makes the system more expensive and may require a higher level of maintenance. or the fourth state of matter.

(6) Joint design. particularly on heavy wall pipe. (5) Another method of welding with plasma is the keyhole method of welding. Figure 10-38 shows various joint designs that can be welded by the plasma arc process. For root pass work. This method of operation is used for welding extremely thin material. This results in faster welding speeds and deeper weld penetration.columnar form and is parallel sided so that it does not flare out in the same manner as the gas tungsten arc. (c) When using the melt-in mode of operation for thick materials. (b) For the melt-in method of operation for welding thin gauge.. the U groove design is used. causes this to happen faster.020 in. The keyhole method can be used only for joints where the plasma can pass through the joint. the same general joint detail as used for shielded metal arc welding and gas tungsten arc welding can be employed.6 to 12. It is used for base metals 1/16 to 1/2 in. In this way. It is affected by the base metal composition and the welding gases. For the keyhole method. the square groove weld should be utilized. This high temperature arc. the joint design is restricted to full-penetration types. The higher-temperature plasma. however. (3. will melt the base metal surface and the filler metal that is added to make the weld. This is similar to the gas tungsten arc. (0. (a) Joint design is based on the metal thicknesses and determined by the two methods of operation.020 in.0 mm) in thickness. and for lap joints using arc spot welds and arc seam welds.130 mm) to 0.500 mm) to 0. and for welding multipass groove and welds and fillet welds. The preferred joint design is the square groove. For welding foil thickness. (0. or keyhole. (2. Surface tension forces the molten base metal to flow around the keyhole to form the weld.0500 mm). the edge flange joint should be used. (4) The high temperature of the plasma or constricted arc and the high velocity plasma jet provide an increased heat transfer rate over gas tungsten arc welding when using the same current. The root face should be 1/8 in. The flanges are melted to provide filler metal for making the weld.
.100 in. It can be used for fillets. The plasma jet penetrates through the workpiece and forms a hole.2 mm) to allow for full keyhole penetration.500 mm) metals. when directed toward the work. with no minimum root opening. The keyhole method provides for full penetration single pass welding which may be applied either manually or automatically in all positions. flange welds. all types of groove welds. and is known as the melt-in mode of operation. (1. Figure 10-36 shows a cross-sectional view of the plasma arc torch head. etc. the plasma acts as an extremely high temperature heat source to form a molten weld puddle. (0. 0.005 in. 0.

it is added in the same manner as gas tungsten arc welding. Equipment must be properly adjusting so that the
. There are two gas systems. The welding circuit for plasma arc welding is more complex than for gas tungsten arc welding. However. just high enough to maintain a stable pilot arc. the pilot arc may be all that is necessary.
(8) Tips for Using the Process.(7) Welding circuit and current. one to supply the plasma gas and the second for the shielding gas. The pilot arc current must be kept sufficiently low. When welding extremely thin materials in the foil range. (b) When filler metal is used. The welding circuit for plasma arc welding is shown by figure 10-39. (a) The tungsten electrode must be precisely centered and located with respect to the orifice in the nozzle. An extra component is required as the control circuit to aid in starting and stopping the plasma arc. The same power source is used. Direct current of a constant current (CC) type is used. Alternating current is used for only a few applications. with the torch-to-work distance a little greater there is more freedom for adding filler metal.

but can be added automatically. helium. Quality. either argon. In addition.
e. and Variables. depending on torch size and application. The filler metal rod size depends on the base metal thickness and welding current. Deposition Rates. (1) Filler metal is normally used except when welding the thinnest metals. cooling water is required.5 liters per minute) up to 5 cu ft per hour (2. Filler Metal and Other Equipment.4 liters per minute) for welding. Overhead position welding requires a slightly higher flow rate. Argon is more common because it is heavier and provides better shielding at lower flow rates. Plasma gas flow also has an important effect. f. For flat and vertical welding. Proper gases must also be used.shielding gas and plasma gas are in the right proportions. The filler metal is usually added to the puddle manually. Composition of the filler metal should match the base metal. (2) Plasma and shielding gas. a shielding gas flow of 15 to 30 cu ft per hour (7 to 14 liters per minute) is sufficient. Active gases are not recommended for plasma gas. (c) Heat input is important. or a mixture. is used for shielding the arc area from the atmosphere. (1) The quality of the plasma arc welds is extremely high and usually higher than gas tungsten arc welds because there is little or no possibility of tungsten inclusions in the
. Argon is used for plasma gas at the flew rate of 1 cu ft per hour (0. An inert gas. These factors are shown by figure 10-40.

Most of the variables shown for plasma arc are similar to the other arc welding processes. The major variables exert considerable control in the process. Variables such as the angle and setback of the electrode and electrode type are considered fixed for the application. All variables should appear in the welding procedure. Deposition rates for plasma arc welding are somewhat higher than for gas tungsten arc welding and are shown by the curve in figure 10-41.weld. There are two exceptions: the plasma gas flow and the orifice diameter in the nozzle.
(2) The process variables for plasma arc welding are shown by figure 10-41. or
. The minor variables are generally fixed at optimum conditions for the given application. The plasma arc process does respond differently to these variables than does the gas tungsten arc process. The standoff. Weld schedules for the plasma arc process are shown by the data in table 10-5.

(2) Programmed welding can also be employed for plasma arc welding in the same manner as it is used for gas tungsten arc welding. The "hot wire" concept can be used. it is often necessary to program the plasma gas flow. Figure 10-42 shows typical air-cooled carbon electrode holders. Water-cooled holders are available for use with the larger size electrodes.torch-to-work distance. or adapters can be fitted to regular holders to permit accommodation of the larger electrodes. g. The complexity of the programming depends on the needs of the specific application. Equipment.
. is less sensitive with plasma but the torch angle when welding parts of unequal thicknesses is more important than with gas tungsten arc. Carbon electrodes range in size from 1/8 to 7/8 in. This is particularly important when closing a keyhole which is required to make the root pass of a weld joining two pieces of pipe.2 mm) in diameter. Variations of the Process. Pulsing can be accomplished by the same apparatus as is used for gas tungsten arc welding. General. (3. Pressure and/or filler metal may or may not be used.2 to 22. (1) The welding current may be pulsed to gain the same advantages pulsing provides for gas tungsten arc welding. Carbon arc welding is a process in which the joining of metals is produced by heating with an arc between a carbon electrode and the work. The same power source with programming abilities is used and offers advantages for certain types of work. This means that low-voltage current is applied to the filler wire to preheat it prior to going into the weld puddle. Baked carbon electrodes last longer than graphite electrodes. A high current pulse is used for maximum penetration but is not on full time to allow for metal solidification. This gives a more easily controlled puddle for out-of-position work. b. In addition to programming the welding current. CARBON ARC WELDING (CAW) a. No shielding is used. (1) Electrodes. (3) The method of feeding the filler wire with plasma is essentially the same as for gas tungsten arc welding. 10-11.

The power source is the conventional or constant current type with drooping volt-amp characteristics. The electrode should be adjusted often to compensate for the erosion of carbon. The power source should have a voltage rating of 50 volts. which could be absorbed by the weld metal. since this voltage is used when welding copper with the carbon arc. If the electrode were positive. and the conventional electrode holder will not efficiently hold and transmit current to the carbon electrode. It is used for welding copper.(2) Machines. When welding thinner materials. c. This type of holder is used because the carbon electrodes become extremely hot in use. It is also used for making bronze repairs on cast iron parts. since it can be used at high currents to develop the high heat usually required.0 to 5. (1) The single electrode carbon arc welding process is no longer widely used. the positive pole (anode) is the pole of maximum heat. Direct current welding machines of either the rotating or rectifier type are power sources for the carbon arc welding process. In the carbon steel arc. In this case. the carbon electrode would erode very rapidly because of the higher heat. (3) Welding circuit and welding current. a 60 percent duty cycle power source is utilized.0 mm) of the carbon electrode should protrude through the holder towards the arc. Carbon arc welding is also used for joining galvanized steel. The difference in the apparatus is a special type of electrode holder used only for holding carbon electrodes.0 in. Advantages and Major Uses. (76. the process is used for making autogenous welds. and would cause black carbon smoke and excess carbon. (b) Single electrode carbon arc welding is always used with direct current electrode negative (DCEN). Alternating current is not recommended for single-electrode carbon arc welding.
. or straight polarity. the bronze filler rod is added by placing it between the arc and the base metal. Normally. From 3.2 to 127. (a) The welding circuit for carbon arc welding is the same as for shielded metal arc welding. or welds without added filler metal.

Since the carbon arc is used primarily as a heat source to generate a welding puddle. it can be used on metals that are not affected by carbon pickup or by the carbon monoxide or carbon dioxide arc atmosphere. The main use of carbon arc welding of steel is making edge welds without the addition of filler metal. A bronze welding rod is used.
. Galvanized steel can be braze welded with the carbon arc. This is done mainly in thin gauge sheet metal work. and. It is an all-position welding process. (1) Steels.(2) The carbon arc welding process has been used almost entirely by the manual method of applying. (2) Cast iron. Table 10-7 shows the welding position capabilities.
d. It can be used for welding steels and nonferrous metals. where the edges of the work are fitted closely together and fused using an appropriate flux. The casting should be preheated to about 1200°F (649°C) and slowly cooled if a machinable weld is desired. a short arc length. such as tanks. Weldable Metals. and for surfacing. Table 106 shows the normal method of applying carbon-arc welding. rapid travel speed should be used. The arc is directed on the rod so that the galvanizing is not burned off the steel sheet. The welding rod should melt and wet the galvanized steel. The arc should be started on the welding rod or a starting block. Iron castings may be welded with the carbon arc and a cast iron welding rod. Low current. Carbon arc welding is primarily used as a heat source to generate the weld puddle which can be carried in any position.

paint. oil. (3. (3. is of the same composition as the base metal. the arc should be used to locally preheat the weld area. in disintegrating. as shown in figure 10-43. a weld is produced. (3) The workpieces must be free from grease. A long arc length should be used to permit carbon from the electrode to combine with oxygen to form carbon dioxide. As the molten metal solidifies.(3) Copper. uses a single electrode with the arc between it and the base metal. Reverse polarity will produce carbon deposits on the work that inhibit fusion. and is not popular today. They may be tack welded together. which will provide some shielding of weld metal.
. Filler metal. The two pieces should be clamped tightly together with no root opening. e. (4) Carbon electrodes 1/8 to 5/16 in. also melts the filler rod. A root opening of 1/8 in. The end of the electrode should be prepared with a long taper to a point. Straight polarity should always be used for carbon arc welding of copper. Bronze filler metal can be used for brazing and braze welding. Principles of Operation.2 mm) is recommended. when used. The work should be preheated in the range of 300 to 1200°F (149 to 649°C) depending upon the thickness of the parts. Best results are obtained at high travel speeds with the arc length directed on the welding rod.2 to 7. and other foreign matter. The nonconsumable graphite electrode erodes rapidly and.9 mm) in diameter may be used. scale. produces a shielding atmosphere of carbon monoxide and carbon dioxide gas. when required. It is the oldest arc process. The diameter of the point should be about half that of the electrode. depending upon the current required for welding.
(2) In carbon arc welding. the arc heat between the carbon electrode and the work melts the base metal and. (1) Carbon arc welding. The high thermal conductivity of copper causes heat to be conducted away from the point of welding so rapidly that it is difficult to maintain welding heat without preheating. If this is impractical. These gases partially displace air from the arc atmosphere and prohibit the oxygen and nitrogen from coming in contact with molten metal.

This could cause a hard spot in the weld at the point of contact. Welding vertically or overhead with the carbon arc is difficult because carbon arc welding is essentially a puddling process. (8) For outside corner welds in 14 to 18 gauge steel sheet. Such welds are usually smother and more economical to make than shielded metal arc welds made under similar conditions. The welding schedule for carbon arc welding galvanized iron using silicon bronze filler metal is given in table 10-8.For steel. there is likely to be excessive carburization of the molten metal resulting in a brittle weld. The arc is directed on the surface of the work and gradually moved along the joint. f. Welding schedules.0 mm) from the electrode holder. the welding rod is fed into the molten weld pool with one hand while the arc is manipulated with the other. In general.5 mm) is best.4 and 9. The weld joint should be backed up. Progress along the weld joint and the addition of a welding rod must be timed to provide the size and shape of weld bead desired. For welding copper. (6) When the arc is broken for any reason. it should not be restarted directly upon the hot weld metal. the carbon arc can be used to weld the two sheets together without a filler metal.0 in. an arc length between 1/4 and 3/8 in. (6. especially in the case of thin sheets. to support the molten weld pools and prevent excessive melt-thru. Table 1010 shows the welding current to be used for each size of the two types of carbon electrodes.6 to 127. use a high arc voltage and follow the schedule given in table 10-9. (101. the electrode should protrude about 4. The arc should be started on cold metal to one side of the joint. If the arc length is too short. The arc must be directed on the filler wire which will melt and flow on to the joint.0 to 5.
. and then quickly returned to the point where welding is to be resumed. (5) A carbon arc may be struck by bringing the tip of the electrode into contact with the work and immediately withdrawing it to the correct length for welding. A short arc should be used to avoid damaging the galvanizing. (7) When the joint requires filler metal. constantly maintaining a molten pool into which the welding rod is added in the same manner as in gas tungsten arc welding.

g.
. Variations of the Process.

(3) Carbon arc cutting is an arc cutting process in which metals are severed by melting them with the heat of an arc between a carbon electrode and the base metal. The carbon electrodes are held in the holder by means of set screws and are adjusted so they protrude equally from the clamping jaws. One is twin carbon arc welding. The twin carbon electrode method is relatively slow and does not have much use as an industrial welding process. Direct current power can be used. (a) The twin carbon electrode holder is designed so that one electrode is movable and can be touched against the other to initiate the arc. The arc gap or spacing between the two electrodes most be adjusted more or less continuously to provide the fan shape arc. (c) The twin carbon arc can be used for many applications in addition to welding. The process can also be used for brazing. brazing. but when it is.(1) There are two important variations of carbon arc welding. It can be used as a heat source to bend or form metal. and soldering. With alternating current. The temperature of this arc flame is between 8000 and 9000°F (4427 and 4982°C). The welding current settings or schedules for different size of electrodes is shown in table 10-11. (2) Twin carbon arc welding is an arc welding process in which the joining of metals is produced. (b) Alternating current is used for the twin carbon welding arc. Filler metal may or may not he used. The process
. by heating with an electric arc maintained between two carbon electrodes. When the two carbon electrodes are brought together. the arc is struck and established between them. using a special electrode holder. It is softer than that of the single carbon arc. The angle of the electrodes provides an arc that forms in front of the apex angle and fans out as a soft source of concentrated heat or arc flame. the electrode connected to the positive terminal should be one size larger than the electrode connected to the negative terminal to ensure even disintegration of the carbon electrodes. The other is carbon arc cutting and gouging. the electrodes will burn off or disintegrate at equal rates.

The process is relatively slow. The term MIG welding is still more commonly used. GAS METAL-ARC WELDING (GMAW OR MIG WELDING) a. The process is sometimes referred to as MIG or CO2 welding. Equipment. and the use of reactive gases. a shielding gas supply. (1) Gas metal arc welding equipment consists of a welding gun. and automatic modes. It is utilized particularly in high production welding operations. as shown in figure 1044. application to a broader range of materials. All commercially important metals such as carbon steel. This latter development has led to the formal acceptance of the term gas metal arc welding (GMAW) for the process because both inert and reactive gases are used. and a wire-drive system which pulls the wire electrode from a spool
. or gas mixtures. and is used only when other cutting equipment is not available. Recent developments in the process include operation at low current densities and pulsed direct current. b. electrode. stainless steel. Gravity causes the molten metal to fall away to produce the cut. and welding conditions. results in a ragged cut. (1) Gas metal arc welding ( GMAW or MIG welding) is an electric arc welding process which joins metals by heating them with an arc established between a continuous filler metal (consumable) electrode and the work. General. 10-12. a power supply. particularly CO2. and copper can be welded with this process in all positions by choosing the appropriate shielding gas.
(2) MIG welding is operated in semiautomatic. aluminum. machine. Shielding of the arc and molten weld pool is obtained entirely from an externally supplied gas or gas mixture.depends upon the heat input of the carbon arc to melt the metal.

(b) Constant voltage power supply.
(2) Two types of power sources are used for MIG welding: constant current and constant voltage. which transfers current from a power source to the arc. operate the welding contactor. The MIG process is used for semiautomatic. and automatic welding. A source of cooling water may be required for the welding gun. (a) Constant current power supply. The speed of the electrode drive is used to control the average welding current. Constant current power sources are not normally selected for MIG welding because of the control needed for electrode feed speed. Semiautomatic MIG welding is often referred to as manual welding. With this type. machine. Arc length (voltage) is controlled by the automatic adjustment of the electrode feed rate. This type of welding is best suited to large diameter electrodes and machine or automatic welding. a system of accurate controls is employed to initiate and terminate the shielding gas and cooling water. The arc voltage is established by setting the output voltage on the power supply. While simple in principle. and control electrode feed speed as required. In passing through the gun. However. where very rapid change of electrode feed rate is not required. The power source will supply the necessary amperage to melt the welding electrode at the rate required to maintain the present voltage or relative arc length.and pushes it through a welding gun. the welding current is established by the appropriate setting on the power supply. This characteristic is generally preferred for the
. Most constant current power sources have a drooping volt-ampere output characteristic. the wire becomes energized by contact with a copper contact tube. The basic features of MIG welding equipment are shown in figure 1045. The systems are not self-regulating. true constant current machines are available.

The conventional pistol type holder is also used for arc spot welding applications where filler metal is required. The orifice usually varies from approximately 3/8 to 7/8 in. A typical semiautomatic gas-cooled gun is shown in figure 10-46. With a pulsed direct current power supply. Sometimes they are shaped similar to an oxyacetylene torch. internal circulating water. where the most cooling is necessary. Cooling is required to remove the heat generated within the gun and radiated from the welding arc and the molten weld metal. Shielding gas. Guns are equipped with metal nozzles of various internal diameters to ensure adequate gas shielding. or both. The nozzles are usually threaded to make replacement easier. This type of gun is designed for small diameter wires and is flexible and maneuverable. The welding control is designed to regulate the flow of cooling water and the supply of shielding gas. (4) Welding guns. In some versions of the pistol design. The use of this type of power supply in conjunction with a constant wire electrode feed results in a self-correcting arc length system. The curved gun uses a curved current-carrying body at the front end. An electrical switch is needed to start and stop the welding current. a welding gun must have a sliding electrical contact to transmit the welding current to the electrode. It is suited for welding in tight. The gun must also have a gas passage and a nozzle to direct the shielding gas around the arc and the molten weld pool. (3) Motor generator or dc rectifier power sources of either type may be used. Welding guns for MIG welding are available for manual manipulation (semiautomatic welding) and for machine or automatic welding. the power source pulses the dc output from a low background value to a high peak value. are used for cooling. hand-held guns are usually similar to a pistol in shape. depending upon welding requirements.welding of all metals. Because the electrode is fed continuously. Because the average power is lower. the electrode feed system. (a) Semiautomatic guns. with electrode wire fed through the barrel or handle. water is directed through passages in the gun to cool both the contact tube and the metal shielding gas nozzle. (10 to 22 mm). through which the shielding gas is brought to the nozzle.
. pulsed welding current can be used to weld thinner sections than those that are practical with steady dc spray transfer. Semiautomatic. hard to reach corners and other confined places. The pistol grip handle permits easy manual loading of the holder against the work. and shielding gas flow. The heavy nozzle of the holder is slotted to exhaust the gases away from the spot. It is also designed to prevent the wire freezing to the weld by timing the weld over a preset interval.

A gun that has a self-contained wire feed mechanism and electrode wire supply.45 to 1. A gun that has the electrode wire fed to it through a flexible conduit from a remote wire feeding mechanism.9 mm) are normally used with this type of gun. These guns are available for service up to 600 amperes. The system permits the use of flexible conduits in lengths up to 50 ft (15 m) or more from the remote wire feeder.7 m) flexible conduit. (7. 2. 3. Air-cooled guns are available for applications where water is not readily obtainable as a cooling medium. (c) Water-cooled guns for manual MIG welding similar to gas-cooled types with the addition of water cooling ducts.9 mm) can be used with these types of feed mechanisms. Wire diameters of 3/10 to 15/32 in. The holder is generally pistol-like and its operation is similar to the water-cooled type. with carbon dioxide shielding gas. Steel wires of 7/20 to 15/16 in. It can also be used in a push-pull type feeding system.(b) Air cooled guns.19 to 3. (1. and it is not limited by a 12 ft (3. 1. (102 mm) diameter. The ducts circulate water around the contact tube and the gas nozzle. intermittent duty.7 m) length range due to the wire feeding limitations of a push-type system. Water cooling permits the gun to operate continuously at rated capacity and at lower temperatures. However. (8. The wire supply is generally in the form of a 4 in. A pull-type gun that has the electrode wire fed to it through a flexible conduit from a remote spool.6 to 11. Aluminum and steel electrodes with diameters of 3/10 to 5/8 in.6 to 15.1 kg) spool. 1 to 2-1/2 lb (0. Three general types of air-cooled guns are available. (7. The conduit is generally in the 12 ft (3. This type of gun employs a pull-type wire feed system. Water-coded guns are used for
. they are usually limited to 200 amperes with argon or helium shielding.8 mm) diameter and aluminum wires of 3/64 to 1/8 in.18 mm) diameter can be fed with this arrangement.9 to 23. This incorporates a self-contained wire feeding mechanism.

parts.and fully automatic. (1) Arc power and polarity. copper. dcsp (electrode
. Air-cooled guns are heavier than water-cooled guns of the same welding current capacity. and structures. smooth metal transfer. (3) The gas shield protects the arc so that there is very little loss of alloying elements as the metal transfers across the arc. (a) The vast majority of MIG welding applications require the use of direct current reverse polarity (electrode positive). weld joint design. When employed. MIG welding is widely used by many industries for welding a broad variety of materials. relatively low spatter loss. materials. including aluminum. Only minor weld spatter is produced. Direct current straight polarity (electrode negative) is seldom used. since the arc can become unstable and erratic even though the electrode melting rate is higher than that achieved with dcrp (electrode positive). c. magnesium. Disadvantages. and it is easily removed. and many of their alloys.or water-cooled guns is based on the type of shielding gas. (1) The major advantage of gas metal-arc welding is that high quality welds can be produced much faster than with SMAW or TIG welding. d. e. and existing shop practice. air-cooled guns are easier to manipulate to weld outof-position and in confined areas.applications requiring 200 to 750 amperes. there is no chance for the entrapment of slag in the weld metal. This type of electrical connection yields a stable arc. Advantages. (4) This process is versatile and can be used with a wide variety of metals and alloys. as well as iron and most of its alloys. including semi. The process can be operated in several ways. (d) The selection of air. (2) The equipment is complex compared to equipment used for the shielded metal-arc welding process. (2) Since a flux is not used. However. and good weld bead characteristics for the entire range of welding currents used. nickel. (1) The major disadvantage of this process is that it cannot be used in the vertical or overhead welding positions due to the high heat input and the fluidity of the weld puddle. The water in and out lines to the gun add weight and reduce maneuverability of the gun for welding. Process Principles. welding current range.

The factors having the most influence are: 1. direction of drops (axial or nonaxial). 4. (a) Filler metal can be transferred from the electrode to the work in two ways: when the electrode contacts the molten weld pool. Penetration is lower with straight polarity than with reverse polarity direct current. (c) Axially directed transfer refers to the movement of drops along a line that is a continuation of the longitudinal axis of the electrode. and it may not reignite if the cathode cools sufficiently. Electrode composition. Shielding gas. out-of-position welding. Current density. (3) Short circuiting transfer. When weld heat input is extremely low. Power supply characteristics. This type of transfer produces a small. Magnitude and type of welding current. and when discrete drops are moved across the arc gap under the influence of gravity or electromagnetic forces. 5. and filling of large root openings. fast-freezing weld pool that is generally suited for the joining of thin sections.negative) is used in conjunction with a "buried" arc or short circuiting metal transfer. Electrode extension. and type of transfer are determined by a number of factors. Nonaxially directed transfer refers to movement in any other direction. (b) Alternating current has found no commercial acceptance with the MIG welding process for two reasons: the arc is extinguished during each half cycle as the current reduces to zero. (b) Shape. (2) Metal transfer. which is known as short circuiting transfer (short circuiting arc welding). plate distortion is small. Metal is transferred from the
. thereby establishing a short circuit. (a) Short circuiting arc welding uses the lowest range of welding currents and electrode diameters associated with MIG welding. 3. 6. Drop transfer can be either globular or spray type. size. and rectification of the reverse polarity cycle promotes the erratic arc operation. 2.

shielding gas has very little effect on this type of transfer. Globular transfer is characterized by a drop size of greater diameter than that of the electrode. The molten drop grows until it detaches by short circuiting or gravity. the resulting weld is likely to be unacceptable because of lack of fusion. The most important of these are pinch force and anode reaction force. It should not occur so fast that it causes spatter by disintegration of the transferring drop of filler metal. the wire electrode is melted by the arc heat conducted through the molten drop. axially directed transfer can be achieved in a substantially inert gas shield without spatter. insufficient penetration. globular transfer takes place when the current density is relatively low. the current increases. The open circuit voltage of the power source must be low enough so that an arc cannot continue under the existing welding conditions. This is due to an electromagnetic repulsive force acting upon the bottom of the molten drops. The rate of current increase is controlled by adjustment of the inductance in the power source. (c) As metal transfer only occurs during short circuiting. It would continue to increase if an arc did not form. However. The arc length must be long enough to assure detachment of the drop before it contacts the molten metal. However. A portion of the energy for arc maintenance is provided by the inductive storage of energy during the period of short circuiting. It is usually caused either by gas evolution or electromagnetic forces on the molten tip of the electrode. The electrode tip is not enveloped by the arc plasma. (a) With a positive electrode (dcrp). With CO2 shielding. and excessive reinforcement. (b) The electrode contacts the molten weld pool at a steady rate in a range of 20 to over 200 times each second. regardless of the type of shielding gas. (5) Spray transfer. (b) Globular. Flow of electric current through the electrode generates several forces that act on the molten tip. As the wire touches the weld metal. (4) Globular transfer.electrode to the work only during a period when the electrode is in contact with the weld pool. (c) Carbon dioxide shielding always yields nonaxially directed globular transfer. carbon dioxide (CO2) shielding yields this type of transfer at all usable welding currents. The magnitude of the pinch force is a direct function of welding current and wire diameter. The value of inductance required depends on both the electrical resistance of the welding circuit and the temperature range of electrode melting. and is usually responsible for drop detachment. There is no metal transfer across the arc gap.
. The rate of current increase must be high enough to maintain a molten electrode tip until filler metal is transferred. Spatter can occur.

For all metals. (b) Spray type transfer has a typical fine arc column and pointed wire tip associated with it. The reduction in droplet size is also accompanied by an increase in the rate of droplet detachment. When the transfer is gravitational.(a) In a gas shield of at least 80 percent argon or helium. (a) In free-flight transfer. In the projected type of transfer. The metal spray is axially directed. the drops are detached by gravity alone and fall slowly through the arc column. the liquid drops that form at the tip of the consumable electrode are detached and travel freely across the space between the electrode and work piece before plunging into the weld pool. as illustrated in figure 10-47. Metal transfer rate may range from less than 100 to several hundred droplets per second as the electrode feed rate increases from approximately 100 to 800 in.
(6) Free flight transfer. other forces give the drop an initial acceleration and project it independently of gravity toward the weld pool. Molten filler metal transfers across the arc as fine droplets./min (42 to 339 mm/s). forces act on the liquid drop and give it an initial velocity directly away from the weld pool. the change takes place at a current value called the globular-to-spray transition current. During repelled transfer. The gravitational and projected ties of free-
. filler metal transfer changes from globular to spray type as welding current increases for a given size electrode. The droplet diameter is equal to or less than the electrode diameter.

overcame the repelling forces. which is some distance from the gun. (7) Welding parameters. Direct current reversedpolarity is recommended for the MIG welding process. wires of these alloys melt slowly. Figures 10-48 through 10-54 show the relationship between the voltage and the current levels. producing a more uniform weld bead and reducing undercut. As the current increases. In this case. separating force increases. nickel alloys. Some manual welding guns contain the wire-driving mechanism within the gun itself. electrode-positive (reverse polarity) arc and properly selected types of shielding gases. When carbon dioxide is used as the shielding gas. primarily electrical. Another manual gun design combines feed mechanisms within the gun and at the wire supply itself. This causes an excessive amount of spatter. where it picks up the welding current. A large spherical drop forms at the tip and is detached when the force due to gravity exceeds that of surface tension. At higher currents. Electrodes designed to be used with carbon dioxide shielding gas require extra deoxidizers in their formulation because in the heat of the arc. and the type of transfer across the arcs. At a certain current. the drop appears to be repelled from the work electrode and is eventually detached while moving away from the workpiece and weld pool. Other guns require that the wire-feeding mechanism be located at the spool of wire. previously bell-shaped or spherical and having relatively low brightness. Carbon dioxide is also used as a shielding gas because it is cheaper than argon and argon-oxygen mixtures. the electromagnetic force becomes significant and the total. but require precautions such as a special coating on the electrode wire or special shield gas mixtures. the type of metal transfer is much different. (b) At low currents. At low and medium reversed-polarity currents.flight metal transfer may occur in the gas metal-arc welding of steel. becomes narrower and more conical and has a bright central core. Argon is the shielding gas used most often. The arc column.
. the carbon dioxide dissociates to carbon monoxide and oxygen. the transfer is less irregular because other forces. Straight polarity and alternating current can be used. The rate at which drops are formed and detached also increases. This stabilizes the arc and promotes a better wetting action. The droplets that form at the wire tip become elongated due to magnetic pressure and are detached at a much higher rate. the wire is driven through a flexible conduit to the welding gun. a change occurs in the character of the arc and metal transfer. which can cause oxidation of the weld metal. (c) The filler wire passes through a copper contact tube in the gun. Small amounts of oxygen (2 to 5 percent) frequently are added to the shielding gas when steel is welded. or aluminum alloys using a direct current.

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(1) The welding procedures for MIG welding are similar to those for other arc welding processes.f. All gas and water connections should be tight. It should be designed for easy loading and unloading. (3) The assembly of the welding equipment should be done according to the manufacturer’s directions. Adequate fixturing and clamping of the work are required with adequate accessibility for the welding gun. Copper backing bars are removable. The position of the electrode with respect to the weld joint is important in order to obtain the desired joint penetration. Fixturing must hold the work rigid to minimize distortion from welding. (2) When complete joint penetration is required. A backing strip. some method of weld backing will help to control it. Welding Procedures. Porosity may also occur. there should be no leaks. backing weld. Electrode positions for automatic MIG welding are similar to those used with submerged arc welding. (4) The gun nozzle size and the shielding gas flow rate should be set according to the recommended welding procedure for the material and joint design to be welded. Joint designs that require long nozzle-to-work distances will need higher gas flow rates than
. Backing strips and backing welds usually are left in place. and weld bead geometry. Aspiration of water or air into the shielding gas will result in erractic arc operation and contamination of the weld. particularly when welding ferromagnetic materials such as steel. Location of the connection is important. or copper backing bar can be used. fusion. The best direction of welding is away from the work lead connection. Good connection of the work lead (ground) to the workpiece or fixturing is required.

should be adjusted to give good arc starting and smooth arc operation with minimum spatter. depending on the application. It is important to keep the electrode extension (nozzleto-work distance) as uniform as possible during welding. (5) The gun contact tube and electrode feed drive rolls are selected for the particular electrode composition and diameter. shielding gas. A trial bead weld should be made to establish proper voltage (arc length) and feed rate values. Therefore. The optimum settings will depend on the equipment design and controls. The extension used is related to the type of MIG welding. short circuiting or spray type transfer. flush with. FLUX-CORED ARC WELDING (FCAW) a. the welding current will be establish by the electrode feed rate. and must be replaced periodically if good electrical contact with electrode is to be maintained and heating of the gun is to be minimized. or extending beyond the gas nozzle. When welding is done in confined areas or in the root of thick weld joints. inductance.those used with normal nozzle-to-work distances. metal transfer. (1) Flux-cored. as specified by the equipment manufacturer. and welding speed. the contact tube may be inside. (6) Electrode extension is set by the distance between the tip of the contact tube and the gas nozzle opening. welding position.
. base metal composition and thickness. General. Other variables. small size nozzles are used. 10-13. (7) The electrode feed rate and welding voltage are set to the recommended values for the electrode size and material. weld joint design. such as slope control. tubular electrode welding has evolved from the MIG welding process to improve arc action. and weld appearance. The gas nozzle should be of adequate size to provide good gas coverage of the weld area. With a constant voltage power source. The contact tube will wear with usage. Shielding is obtained by a flux contained within the tubular electrode wire or by the flux and an externally supplied shielding gas. A diagram of the process is shown in figure 10-55. electrode material and size. or both. weld metal properties. It is an arc welding process in which the heat for welding is provided by an arc between a continuously fed tubular electrode wire and the workpiece.

controls. are added to the basic equipment. and welding cables. several items. (1) The equipment used for flux-cored arc welding is similar to that used for gas metal arc welding. A major difference between the gas shielded electrodes and the self-shielded electrodes is that the gas shielded wires also require a gas shielding system. the arc is smooth and more manageable when compared in using large diameter gas metal arc welding electrodes with carbon dioxide. Since the filler metal transfers across the arc. The basic arc welding equipment consists of a power source. Fume extractors are often used with this process. At high welding currents.(2) Flux-cored arc welding is similar to gas metal arc welding in many ways. This may also have an effect on the type of welding gun used. Figure 10-56 shows a diagram of the equipment used for semiautomatic flux-cored arc welding. some spatter is created and some smoke produced.
. such as seam followers and motion devices. wire feeder. Flux-cored arc welding is widely used for welding ferrous metals and is particularly good for applications in which high deposition rates are needed. A slag coating is left on the surface of the weld bead. welding gun. The fluxcored wire used for this process gives it different characteristics. b. The arc and weld pool are clearly visible to the welder. Equipment. For machines and automatic welding. which must be removed.

(2) The power source. but machines that operate on 200 or 575 volt input are also available. (3) Flux-cored arc welding uses direct current. Electrode negative current gives lighter penetration and is used for welding thinner metal or metals where there is poor fit-up. Motor-driven generators produce a very stable arc. which means that they can be used to weld 6 of every 10 minutes. The gasoline or diesel engine-driven welding machines have either liquid or air-cooled engines. or welding machine. Electrode positive current gives better penetration into the weld joint. The power sources generally recommended for flux-cored arc welding are direct current constant voltage type. Direct current can be either reverse or straight polarity. or by an internal combustion engine for field applications. The same power sources used with gas metal arc welding are used with flux-cored arc welding. which indicates they can be used to weld continuously. Power sources may operate on either single phase or three-phase input with a frequency of 50 to 60 hertz. Some self-shielding flux-cored ties are used with DCEP while others are developed for use with DCEN. Flux-cored arc welding generally uses higher welding currents than gas metal arc welding. Some machines used for this process have duty cycles of 60 percent. Flux-cored electrode wires are designed to operate on either DCEP or DCEN. but are noisier. It is important to use a power source that is capable of producing the maximum current level required for an application. Most power sources operate on 230 or 460 volt input power. Most power sources used for flux-cored arc welding have a duty cycle of 100 percent. Both rotating (generator) and static (single or three-phase transformer-rectifiers) are used. which sometimes requires a larger power source. The weld created by DCEN is wider and shallower than the weld produced by DCEP. provides the electric power of the proper voltage and amperage to maintain a welding arc. The wires designed for use with an external gas shielding system are generally designed for use with DCEP. (4) The generator welding machines used for this process can be powered by an electric rotor for shop use. more
.

Water-cooled guns permit more efficient cooling of the gun.
. The gear box and wire feed motor shown in figure 10-57 have form feed rolls in the gear box.expensive. although watercooled guns may also be used. but a shielding gas. and are preferred for many applications using 500 amperes. and require more maintenance than transformerrectifier machines. Water-cooled guns are recommended for use with welding currents greater than 600 amperes. provides additional cooling effects. a voltage sensing circuit is used to maintain the desired arc length by varying the wire feed speed. Aircooled guns are preferred for most applications less than 500 amperes.
(6) Both air-cooled and water-cooled guns are used for flux-cored arc welding. With a variable speed wire feeder. which are used with constant voltage power sources. (5) A wire feed motor provides power for driving the electrode through the cable and gun to the work. (7) Shielding gas equipment and electrodes. Variations in the arc length increase or decrease the wire feed speed. A wire feeder consists of an electrical rotor connected to a gear box containing drive rolls. System selection depends upon the application. when used. Aircooled guns are cooled primarily by the surrounding air. Air-cooled guns are lighter and easier to manipulate. There are several different wire feeding systems available. consume more power. Most of the wire feed systems used for flux-cored arc welding are the constant speed type. A water-cooled gun has ducts to permit water to circulate around the contact tube and nozzle. Welding guns are rated at the maximum current capacity for continuous operation.

control valves. or coke. Active gases such as carbon dioxide. Above the liquid. and argon-carbon dioxide mixtures are used for almost all applications. cost of the gas. A shielding gas displaces air in the arc area. Carbon dioxide. the carbon dioxide is in both a liquid and a vapor form with the liquid carbon dioxide occupying approximately two thirds of the space in the cylinder. a gas regulator. from the manufacturing of ammonia and from the fermentation of alcohol. arc characteristics and metal transfer. The choice of the proper shielding gas for a specific application is based on the type of metal to be welded. When the pressure in the cylinder has dropped to 200 psi (1379 kPa).(a) Shielding gas equipment used for gas shielded flux-cored wires consists of a gas supply hose. The normal discharge rate of the CO2 cylinder is about 10 to 50 cu ft per hr (4. it exists as a vapor gas. argon-oxygen mixture. Inert and active gases may both be used for flux-cored arc welding. With the bulk system. Welding is accomplished under a blanket of shielding gas. The bulk system is normally only used when supplying a large number of welding stations. and supply hose to the welding gun. By weight. the cylinder should be replaced with a new cylinder. if allowed to come in contact with the molten weld metal. The various shielding gases are summarized below. carbon dioxide is usually drawn off as a liquid and heated to the gas state before going to the welding torch. fuel oil. It is also obtained as a by-product of calcining operation in lime kilns. and penetration and weld bead shape. a maximum discharge rate
. When put in high pressure cylinders. (c) The primary purpose of the shielding gas is to protect the arc and weld puddle from contaminating effects of the atmosphere. it exists in both liquid and gas forms. availability.7 to 24 liters per min). Carbon dioxide is manufactured from fuel gases which are given off by the burning of natural gas. 1. Carbon dioxide is the most common. An exception to this is carbon dioxide. it is replaced with carbon dioxide that vaporizes from the liquid in the cylinder and therefore the overall pressure will be indicated by the pressure gauge. As carbon dioxide is drawn from the cylinder. The nitrogen and oxygen of the atmosphere. or in a gas form in high pressure cylinders. A positive pressure should always be left in the cylinder in order to prevent moisture and other contaminants from backing up into the cylinder. this is approximately 90 percent of the content of the cylinder. shielding is accomplished by the decomposition of the electrode core or by a combination of this and surrounding the arc with a shielding gas supplied from an external source. The cylinder is more common. Carbon dioxide is made available to the user in either cylinder or bulk containers. which is almost 100 percent pure. mechanical property requirements. However. In flux-cored arc welding. cause porosity and brittleness. (b) The shielding gases are supplied in liquid form when they are in storage tanks with vaporizers. In the cylinder.

which can be trapped in the weld as porosity deoxidizing elements in the flux core reducing the effects of carbon monoxide formation. These mixtures are often used on low alloy steels and stainless steels.of 25 cu ft per hr (12 liters per min is recommended when welding using a single cylinder. and flowmeter. achieving better arc characteristics. compared to pure carbon dioxide. It also reduces the amount of oxidation that occurs. Argoncarbon dioxide mixtures are often used for out-of-position welding. When flow rate higher than 25 cu ft per hr (12 liters per min) is required. Argon-carbon dioxide mixtures. This loss of carbon can be attributed to the formation of carbon monoxide. If the carbon content in the weld metal is greater than about 0. Because carbon dioxide is an oxidizing gas. silicon. this absorption of heat can lead to freezing of the regulator and flowmeter which interrupts the shielding gas flow. Carbon. carbon dioxide shielding will tend to increase the carbon content of the weld metal. Electrodes that are designed for use with CO2 may cause an excessive buildup of manganese. If flow rates are set too high. deoxidizing elements are added to the core of the electrode wire to remove oxygen. A high percentage of argon gas in the mixture tends to promote a higher deposition efficiency due to the creation of less spatter. Argon and carbon dioxide are sometimes mixed for use with flux-cored arc welding. Most active gases cannot be used for shielding. it absorbs a great deal of heat. The gas mixture produces a fine globular metal transfer that approaches a spray. The oxides formed by the deoxidizing elements float to the surface of the weld and become part of the slag covering. These are deep penetration and low cost. The carbon dioxide shielding gas breaks down into components such as carbon monoxide and oxygen. As the vapor pressure drops from the cylinder pressure to discharge pressure through the CO2 regulator. 2. The weld deposited in an argon-carbon dioxide shield generally has higher tensile and yield strengths. If the carbon content of the weld pool is below about 0. and other deoxidizing elements if they are used with shielding gas mixtures
. The most commonly used gas mixture in flux-cored arc welding is a 75 percent argon-25 percent carbon dioxide mixture. Extra carbon can also reduce the toughness and ductility of some low alloy steels. but carbon dioxide provides several advantages for use in welding steel. carbon dioxide shielding will tend to reduce the carbon content. which can reduce the corrosion resistance of some stainless steels. Some of the carbon dioxide gas will break down to carbon and oxygen. Excessive flow rates can also result in drawing liquid from the cylinder. Carbon dioxide is the most widely used shielding gas for flux-cored arc welding. pressure regulator. normal practice is to manifold two CO2 cylinders in parallel or to place a heater between the cylinder and gas regulator.10 percent.05 percent. Carbon dioxide promotes a globular transfer. is a problem for critical corrosion application.

To form a slag coating that floats on the surface of the weld metal and protects it during solidification. The cores of carbon steel and low alloy electrodes contain primarily fluxing compounds. 3. To provide deoxidizers and scavengers which help purify and produce solid weld-metal. (d) The electrodes used for flux-cored arc welding provide the filler metal to the weld puddle and shielding for the arc. The compounds contained in the electrode perform basically the same functions as the coating of a covered electrode used in shielded metal arc welding. Some of the low alloy steel electrode cores contain high amounts of alloying compounds with a low flux content. To provide arc stabilizers which produce a smooth welding arc and keep spatter to a minimum. Argon-oxygen mixtures containing 1 or 2 percent oxygen are used for some applications. 3. Argon-oxygen mixtures. Shielding is required for sane electrode types. Argon-oxygen mixtures tend to promote a spray transfer which reduces the amount of spatter produced. Self-shielded electrodes contain more fluxing compounds than gas shielded electrodes. 2.containing a high percentage of argon. Most low alloy steel electrodes require gas shielding. A major application of these mixtures is the welding of stainless steel where carbon dioxide can cause corrosion problems. The electrodes for flux-cored arc welding consist of a metal shield surrounding a core of fluxing and/or alloying compounds as shown in figure 10-58. This will have an effect on the mechanical properties of the weld. The sheath comprises approximately 75 to 90 percent of the weight of the electrode. The purpose of the shielding gas is to provide protection from the atmosphere to the arc and molten weld puddle.
. These functions are:
1. will determine the weld metal composition and mechanical properties of the weld. The chemical composition of the electrode wire and flux core. in combination with the shielding gas.

Mechanical properties of the weld metal. An example of a carbon steel electrode classification is E70T-4 where: 1. 2. 4.4. shows the mechanical property requirements for the various carbon steel electrodes. Welding position. 5. Carbon and low alloy steels are classified on the basis of the following items: 1. To provide shielding gas.000 psi (69 MPa). The "E" indicates an electrode. 5. Chemical composition of the weld metal. The second digit or "7" indicates the minimum tensile strength in units of 10. Gas shielded wires require an external supply of shielding gas to supplement that produced by the core of the electrode. Table 10-12. Type of welding current.
. below. (e) The classification system used for tubular wire electrodes was devised by the American Welding Society. 2. Whether or not a CO2 shielding gas is used. 3. To add alloying elements to the weld metal which will increase the strength and improve other properties in the weld metal.

The suffix "4" gives the performance and usability capabilities as shown in table 10-13. The third digit or "0" indicates the welding positions. 4.
. This classification is intended for electrodes not covered by another classification. 5.3. Single pass electrodes do not have chemical composition requirements because checking the chemistry of undiluted weld metal does not give the true results of normal single pass weld chemistry. The chemical composition requirements of the deposited weld metal for carbon steel electrodes are shown in table 10-14. When a "G" classification is used. no specific performance and usability requirements are indicated. A "0" indicates flat and horizontal positions and a "1" indicates all positions. The "T" stands for a tubular or flux cored wire classification.

2.000 psi (552 MPa). In this case it is 80. The "E" indicates electrode.The classification of low alloy steel electrodes is similar to the classification of carbon steel electrodes. The second digit or "8" indicates the minimum tensile in strength in units of 10. The
.000 psi (69 MPa). An example of a low alloy steel classification is E81T1NI2 where: 1.

A "1" indicates all positions and an "0" flat and horizontal position only.3. The "T" indicates a tubular or flux-cored electrode used in flux cored arc welding. 4. 5. The suffix or "Ni2" tells the chemical composition of the deposited weld metal as shown in table 10-17 below. EXXT5-X and EXXT8-X are used with low alloy steel flux-cored electrode classifications. EXXT4-X. The fifth digit or "1" describes the usability and performance characteristics of the electrode. 6. These digits are the same as used in carbon steel electrode classification but only EXXT1-X.
. The third digit or "1" indicates the welding position capabilities of the electrode.

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. The "E" indicates the electrode. 2.The classification system for stainless steel electrodes is based on the chemical composition of the weld metal and the type of shielding to be employed during welding. The digits between the "E" and the "T" indicates the chemical composition of the weld as shown in table 10-18 below. An example of a stainless steel electrode classification is E308T-1 where: 1.

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this cable is often part of the cable assembly.
(8) Welding Cables. The suffix of "1" indicates the type of shielding to be used as shown in table 10-19 below.3. The cable that connects the power source to the welding gun is called the electrode lead. In semiautomatic welding. which also includes the shielding gas hose and
. The "T" designates a tubular or flux cored electrode wire. 4. (a) The welding cables and connectors are used to connect the power source to the welding gun and to the work. These cables are normally made of copper. The cable consists of hundreds of wires that are enclosed in an insulated casing of natural or synthetic rubber.

Flux-cored welding is ideal where bead appearance is important and no machining of the weld is required. Most low-alloy or mild-steel electrodes of the flux-cored type are more sensitive to changes in welding conditions than are SMAW electrodes. Finally. which simplifies the equipment. The cost is less for flux-cored electrodes because the alloying agents are in the flux. A higher percentage of the filler metal is deposited when compared to shield metal arc welding. the electrode lead is normally separate. not in the steel filler wire as they are with solid electrodes. called
. Cable sizes range from the smallest AWG No 8 to AWG No 4/0 with amperage ratings of 75 amperes on up. There is less porosity and greater penetration of the weld with carbon dioxide shielding. better penetration is obtained than from shielded metal arc welding. Flux-cored welding without carbon dioxide shielding can be used for most mild steel construction applications. d. For machine or automatic welding. The electrode wire is fed continuously so there is very little time spent on changing electrodes.the conduit that the electrode wire is fed through. This sensitivity. Some flux-cored wires do not need an external supply of shielding gas. Table 10-20 shows recommended cable sizes for use with different welding currents and cable lengths. The major advantages of flux-cored welding are reduced cost and higher deposition rates than either SMAW or solid wire GMAW. Disadvantages. (b) The size of the welding cables used depends on the output capacity of the welding machine. The cable that connects the work to the power source is called the work lead. and faster travel speeds are often used. The resulting welds have higher strength but less ductility than those for which carbon dioxide shielding is used. The work leads are usually connected to the work by pinchers. It has a high deposition rate. There is less weld spatter than with solid-wire MIG welding.
c. Using small diameter electrode wires. and the distance between the welding machine and the work. A cable that is too small may become too hot during welding. Advantages. welding can be done in all positions. or a bolt. The flux-cored process has increased tolerances for scale and dirt. clamps. the duty cycle of the machine.

Equipment consists of a welding machine or power source. Pressure is not used. or the flux core alone can provide all the shielding gas and slagging materials. Equipment. which appears as a fine line. e. SUBMERGED ARC WELDING (SAW) a. the wire feeder and control system. Submerged arc welding is a process in which the joining of metals is produced by heating with an arc or arcs between a bare metal electrode or electrodes and the work. The flux-cored welding wire. usually a flux recovery system.voltage tolerance. metal powders. in addition to feeding the wire and maintaining the arc length. b. and a travel mechanism for automatic welding. can be decreased if a shielding gas is used. and ferro-alloys. is a hollow tube filled with a mixture of deoxidizers. In semiautomatic welding.
. Flux-cored electrode welding can be done in two ways: carbon dioxide gas can be used with the flux to provide additional shielding. Process Principles. the machinery also provides the joint travel. or electrode. Although flux-cored arc welding may be applied semiautomatically. The closure seam. The welding operator continuously monitors the welding and makes adjustments in the welding parameters. Flux-cored arc welding is also used in machine welding where. the flux hopper and feeding mechanism. Filler metal is obtained from the electrode or from a supplementary welding rod. 10-14. the process is usually applied semiautomatically. by machine. A constant-potential power source and constant-speed electrode feeder are needed to maintain a constant arc voltage. The arc is shielded by a blanket of granular fusible material on the work. the wire feeder feeds the electrode wire and the power source maintains the arc length. is the only visible difference between flux-cored wires and solid colddrawn wire. The welder manipulates the welding gun and adjusts the welding parameters. Automatic welding is used in high production applications. (1) The equipment components required for submerged arc welding are shown by figure 10-59. or automatically. the welding torch for automatic welding or the welding gun and cable assembly for semiautomatic welding. or if the slag-forming components of the core material are increased. General. The carbon dioxide gas shield produces a deeply penetrating arc and usually provides better weld than is possible without an external gas shield. fluxing agents.

The hopper gun may include a start switch to initiate the weld or it may utilize a "hot" electrode so that when the electrode is touched to the work. When constant voltage is used. Multiple electrode systems require specialized types of circuits. Direct current power is used for semiautomatic applications.(2) The power source for submerged arc welding must be rated for a 100 percent duty cycle. If a 60 percent duty cycle power source is used. feeding will begin automatically. especially when ac is employed. but the rectifier machines are more popular. a welding gun and cable assembly are used to carry the electrode and current and to provide the flux at the arc. The electrode wire is fed through the bottom of this flux hopper through a current pickup tip to the arc. the simpler fixed speed wire feeder system is used.
. it must be derated according to the duty cycle curve for 100 percent operation. the voltage sensing electrode wire feeder system must be used. (4) Both generator and transformer-rectifier power sources are used. The flux is fed from the hopper to the welding area by means of gravity. They may be connected in parallel to provide extra power for high-current applications. Welding machines for submerged arc welding range in size from 300 amperes to 1500 amperes. (3) When constant current is used. since the submerged arc welding operations are continuous and the length of time for making a weld may exceed 10 minutes. (5) For semiautomatic application. but alternating current power is used primarily with the machine or the automatic method. A small flux hopper is attached to the end of the cable assembly. either ac or dc. The amount of flux fed depends on how high the gun is held above the work. The CV system is only used with direct current.

(6) For automatic welding. It is widely used in the shipbuilding industry for splicing and fabricating subassemblies. and by many other industries where steels are used in medium to heavy thicknesses. uniform finished weld with no spatter. no involvement of manipulative skills. A flux recovery unit is normally provided to collect the unused submerged arc flux and return it to the supply hopper. (e) no arc flash. weavers. (7) Other pieces of equipment sometimes used may include a travel carriage. the manufacture of machine components for all types of heavy industry. The flux hopper is normally attached to the torch. (g) easy automation for high-operator factor. maintenance. (f) high utilization of electrode wire. c.
. d. This includes the welding of structural shapes. The other limitation is that it is primarily used only to weld mild and low-alloy highstrength steels. It is also used for surfacing and buildup work. Limitations of the Process. (1) The major advantages of the submerged arc welding process are: (a) high quality of the weld metal. (c) smooth. thus minimal need for protective clothing. (8) Submerged arc welding system can become quite complex by incorporating additional devices such as seam followers. the longitudinal seam of larger diameter pipe. (b) extremely high deposition rate and speed. (1) A major limitation of submerged arc welding is its limitation of welding positions. and may have magnetically operated valves which can be opened or closed by the control system. and repair. and the manufacture of vessels and tanks for pressure and storage use. the torch is attached to the wire feed motor and includes current pickup tips for transmitting the welding current to the electrode wire. Advantages and Major Uses. which can be a simple tractor or a complex moving specialized fixture. (2) The submerged arc process is widely used in heavy steel plate fabrication work. and work rovers. (d) little or no smoke. (h) normally.

where the operator monitors the welding operation. Principles of Operation. The submerged arc welding process is a limitedposition welding process. The electrode is fed into the arc automatically from a coil. The flux forms a glass-like slag that is lighter in weight than the deposited weld metal and floats on the surface as a protective cover. (3) In semiautomatic submerged arc welding. The arc is initiated by a fuse type start or by a reversing or retrack system. The welding positions are limited because the large pool of molten metal and the slag are very fluid and will tend to run out of the joint. The heat input limitation of the steel in question must be strictly adhered to when using submerged arc welding. where it becomes the deposited weld metal. The process can be applied semiautomatically. e. The process cannot be applied manually because it is impossible for a welder to control an arc that is not visible. The heat of the arc melts the surface of the base metal and the end of the electrode. The unmelted portion of the flux can be reused. which is laid directly over the weld area. The metal melted off the electrode is transferred through the arc to the workpiece. (1) The submerged arc welding process is shown by figure 10-60. helping to purify and fortify it. Travel can be manual or by machine. the economic advantages may be reduced to the point where flux-cored arc welding or some other process should be considered. The weld is submerged under this layer of flux and slag. slow-cooling cycle can be a problem when welding quenched and tempered steels. Second in popularity is the automatic method. Shielding is obtained from a blanket of granular flux. The flux and slag normally cover the arc so that it is not visible. The most popular method of application is the machine method. The flux close to the arc melts and intermixes with the molten weld metal. In some cases. This may require the making of multipass welds where a single pass weld would be acceptable in mild steel.
(2) Normal method of application and position capabilities. the inability to see the arc and puddle can be a disadvantage in reaching the root of a groove weld and properly filling or sizing. The arc is maintained automatically. this method of application is not too popular. hence the name submerged arc welding. however. It utilizes the heat of an arc between a continuously fed electrode and the work. Welding can be done in the flat position and in the horizontal fillet position with ease.(2) The high-heat input. where welding is a pushbutton operation. Under special
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5 mm) in a single pass and in the flat position. fillet welds can be made up to 1 in. (6. (25 mm) size. Beyond this thickness. (16 mm) thickness.
(4) Joint design.7 mm) can be welded with no edge preparation. different joint details are suggested for maximum utilization and efficiency of submerged arc welding. When welding thicker metal. the square groove design can be used up to 5/8 in. quenched and tempered steels. low-alloy high-strength steels. the maximum thickness is practically unlimited.
Metal thicknesses from 1/16 to 1/2 in. Open roots are used but backing bars are necessary since the molten metal will run through the joint. sometimes called 3 o'clock welding. This information is summarized in table 10-21. For groove welds. it has been used to weld certain copper alloys. (9. (1. (3) Metals weldable and thickness range. Experimentally.4 to 25.4 mm).6 to 12. and many stainless steels. bevels are required. Although the submerged arc welding process can utilize the same joint design details as the shielded metal arc welding process. This requires special devices to hold the flux up so that the molten slag and weld metal cannot run away. The process cannot be used in the vertical or overhead position. Submerged arc welding is used to weld lowand medium-carbon steels. and even uranium. This information is summarized in table 10-22. if a sufficiently
. When multipass technique is used.controlled procedures. With edge preparation. Horizontal fillet welds can be made up to 3/8 in. nickel alloys. it is possible to weld in the horizontal position. welds can be made with a single pass on material from 1/4 to 1 in.

However. Where both sides are accessible. Recommended submerged arc joint designs are shown by figure 10-61 below. to assure full penetration when welding from one side. a backing weld can be made which will fuse into the original weld to provide full penetration. the backing bar may be eliminate. backing bars are recommended.large root face is used.
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The system cannot react instantaneously. (e) For ac welding. (d) The constant current power system is normally used for welding with 5/3 2 in. can be applied when two wires are fed into the arc supplied by a single power source. The constant voltage system.
.2 mm) and smaller diameter electrode wires. and then maintain the preset arc voltage. Direct current is used for most applications which use a single arc. The deposition rate for alternating current is between DCEP and DCEN. the constant current power is always used. There are at least four related factors that control the deposition rate of submerged arc welding: polarity. (a) The welding circuit employed for single electrode submerged arc welding is shown by figure 10-59. The wire feed system must sense the voltage across the arc and feed the electrode wire into the arc to maintain this voltage. The deposition rate is the highest for direct current electrode negative (DCEN). (a) The deposition rates of the submerged arc welding process are higher than any other arc welding process. The polarity of maximum heat is the negative pole. Both direct current electrode positive (DCEP) and electrode negative (DCEN) are used. Deposition rates for single electrodes are shown by figure 10-62. the constant current power system is utilized. and additional electrodes. however. Welding current for submerged arc welding can vary from as low as 50 amperes to as high as 2000 amperes. additives in the flux. When multiple electrode wire systems are used with both ac and dc arcs. long stickout. the wire feed must slow down or speed up to maintain the prefixed voltage across the arc. (3. retract. This adds complexity to the control system. (6) Deposition rates and weld quality.(5) Welding circuit and current. (4 mm) and larger-diameter electrode wires. The control circuit for CC power is more complex since it attempts to duplicate the actions of the welder to retain a specific arc length. (b) The submerged arc welding process uses either direct or alternating current for welding power. (c) The constant voltage type of direct current power is more popular for submerged arc welding with 1/8 in. Most submerged arc welding is done in the range of 200 to 1200 amperes. As conditions change. Arc starting is more complicated with the constant current system since it requires the use of a reversing system to strike the arc. This requires a wire feeder system and a power supply.

This curvature can cause the arc to be struck in a location not expected by the welder. it will float out to the top of the weld. the curvature may cause the arc to be against one side of the weld joint rather than at the root. (d) Several problems may occur when using the semiautomatic application method. The weld will be more uniform and free from inconsistencies. since the weld is hidden and cannot be observed while it is being made. (c) The quality of the weld metal deposited by the submerged arc welding process is high.(b) The deposition rate with any welding current can be increased by extending the "stickout. Uniformity and consistency are advantages of this process when applied automatically. This requires making an extra pass. When using "long stickout" the amount of penetration is reduced. In general. In some
. The electrode wire may be curved when it leaves the nozzle of the welding gun." This is the distance from the point where current is introduced into the electrode to the arc. The weld metal strength and ductility exceeds that of the mild steel or low-alloy base material when the correct combination of electrode wire and submerged arc flux is used. When welding in fairly deep grooves. gases are allowed more time to escape. When submerged arc welds are made by machine or automatically. Additionally. the human factor inherent to the manual welding processes is eliminated. The deposition rates can be increased by metal additives in the submerged arc flux. Flux will be trapped at the root of the weld. the weld bead size per pass is much greater with submerged arc welding than with any of the other arc welding processes. since the submerged arc slag is lower in density than the weld metal. Additional electrodes can be used to increase the overall deposition rate. For this reason. Another problem with semiautomatic welding is that of completely filling the weld groove or maintaining exact size. The heat input is higher and cooling rates are slower. This will cause incomplete root fusion.

defects may occur at the start or at the end of the weld. The reason for the hard weld in carbon and low-alloy steels is too rapid cooling. A simple solution is to avoid placing the parts at a true 45° angle. It should be varied approximately 10° so that the root of the joint is not in line with the centerline of the fillet weld. Excessively hard weld deposits contribute to cracking of the weld during fabrication or during service. which is the centerline of the weld. The best solution is to use runout tabs so that starts and stops will be on the tabs rather than on the product.or overfilled in different areas. the impurities in the melted base metal and in the weld metal all collect at the last point to freeze. or excessive alloy pickup in the weld metal. The submerged arc welding process applied by machine or fully automatically should be done in accordance with welding procedure schedules. too much weld is deposited. If there is sufficient restraint and enough impurities are collected at this point.cases. If the schedules are varied more than 10 percent. Variations in root opening affect the travel speed. This can happen when making large single-pass flat fillet welds if the base metal plates are 45° from flat. (f) Another quality problem has to do with the hardness of the deposited weld metal. A maximum hardness level of 225 Brinell is recommended. assuming that the correct electrode and flux have been selected. If travel speed is uniform. inadequate postweld treatment. or the use of excessively high welding voltages. centerline cracking may occur.
. All of the welds made by this procedure should pass qualification. the weld may be under. show the recommended welding schedules for submerged arc welding using a single electrode on mild and low-alloy steels. The table can be used for welding other ferrous materials. qualification tests should be performed to determine the weld quality. but was developed for mild steel. When these large welds solidify. (e) There is another quality problem associated with extremely large single-pass weld deposits. Table 1023 and figure 10-63. Another solution is to make multiple passes rather than attempting to make a large weld in a single pass. (7) Weld schedules. Excessive alloy pickup is due to selecting an electrode that has too much alloy. High operator skill will overcome this problem. (g) In automatic and machine welding. below. selecting a flux that introduces too much alloy into the weld. tests.

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Multiple passes usually deposit higher-quality weld metal. with several exceptions. (b) In submerged arc welding. depending on the weld metal metallurgy desired. to match the metal being welded. Polarity is established initially and is based on whether maximum penetration or maximum deposition rate is required. The electrode size is related to the weld joint size and the current recommended for the particular joint. Welds for the same joint dimension can be made in many or few passes. The electrode and flux combination selection is based on table 10-24. (a) The welding variables for submerged arc welding are similar to the other arc welding processes. This must also be considered in determining the number of passes or beads for a particular joint.(8) Welding variables. below. the electrode type and the flux type are usually based on the mechanical properties required by the weld.
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The relationship between stickout and deposition rate is shown by figure 10-64. The higher the welding current. however. (25 to 38 mm). the penetration into the base metal decreases. called electrode "stickout. the angle of the work itself. Faster travel speeds produce narrower beads that have less penetration. If speeds are too fast. arc voltage. If the travel speed is too slow. there is a tendency for undercut and porosity. The higher the current. This creates poor bead shape and may cause excessive spatter and flash through the layer of flux. and the distance between the current pickup tip and the arc. the distance between the contact tip and the work is 1 to 1-1/2 in. The welding current should be selected based on the electrode size. If the voltage is too low. As stickout increases. It will have a high crown and the slag will be difficult to remove. the greater the melt-off rate (deposition rate). particularly in the bottom of deep grooves. If the stickout is increased beyond this amount. It has an influence on the bead width and shape.(c) The major variables that affect the weld involve heat input and include the welding current. the thickness of the flux layer. the current should be suitable to produce the size of the weld expected in each pass. Welding current is the most important. the deeper the penetration. Extremely high arc voltage should be avoided. Higher arc voltage also increases the amount of flux consumed. since it can cause cracking. This latter factor.
. For single-pass welds. (d) The arc voltage is varied within narrower limits than welding current. the electrode stays in the weld puddle too long. lowering its ductility. and travel speed. Higher voltages will cause the bead to be wider and flatter. (e) Travel speed influences both bead width and penetration. a very narrow bead will result. This factor must be given serious consideration because in some situations the penetration is required. This can be an advantage for sheet metal welding where small beads and minimum penetration are required. the current should be sufficient for the desired penetration without burn-through. Normally. In multi-pass work. (f) The secondary variables include the angle of the electrode to the work. This is because an abnormal amount of flux is melted and excess deoxidizers may be transferred to the weld deposit." has a considerable effect on the weld. it will cause preheating of the electrode wire. since the weld freezes quicker. which will greatly increase the deposition rate. The low arc voltage produces a stiffer arc that improves penetration.

These welds can be made on the inside or outside diameter. This becomes more of a problem as the diameter of the part being welded gets smaller. (a) One of the major applications for submerged arc welding is on circular welds where the parts are rotated under a fixed head. If the flux depth is too heavy.(g) The depth of the flux layer must also be considered. This dictates that on outside diameters. If it is too thin. the weld may be narrow and humped. Figure 10-65 illustrates these two conditions. the electrode should be angled so that it is ahead of bottom center. Improper electrode position will increase the possibility of slag entrapment or a poor weld surface. there will be too much arcing through the flux or arc flash. (9) Tips for using the process. When the welding is done on the inside circumference. This also may cause porosity. The angle of the electrode should also be changed and pointed in the direction of travel of the rotating part. or 12 o'clock position. so that the weld metal will begin to solidify before it starts the downside slope. These are sometimes called peck marks on the bead surface. Submerged arc welding produces a large molten weld puddle and molten slag which tends to run. the electrode should be positioned ahead of the extreme top. Too many small particles in the flux can cause surface pitting since the gases generated in the weld may not be allowed to escape.
. or the 6 o'clock position.

the bead will have less penetration and will be wider.
. This is based on all other factors remaining the same. If the weld is sloped uphill. This is the travel angle.
(c) The weld will be different depending on the angle of the electrode with respect to the work when the work is level. Figure 10-67 shows the relationship. This information is shown by figure 10-66. the bead will have deeper penetration and will be narrower. If the work is sloped downhill. which can be a drag or push angle. It has a definite effect on the bead contour and weld metal penetration.(b) Sometimes the work being welded is sloped downhill or uphill to provide different types of weld bead contours.

the weld metal will follow and the weld will burn through the joint. Iron powder additions to the flux. 4. When the weld joint is designed with a tight root opening and a fairly large root face. 7. The backing bar holds the weld metal in place until it solidifies. it is necessary to use a backing bar. The molten flux is very fluid and will run through narrow openings. (10) Variations of the process. 3. Two-wire systems--separate power source. If this happens. 5. 6. Electrically "cold" filler wire. The copper backing bars may be water cooled to avoid the possibility of melting and copper pickup in the weld metal. the weld would tend to melt through and the weld metal would fall away from the joint. For thicker materials. If the joint is designed with a root opening and a minimum root face.
. high current and electrode positive should be used. the backing may be submerged arc flux or other specialized type flux. Two-wire systems--same power source. Backing bars are needed whenever there is a root opening and a minimum root face. Long stickout welding. since there is nothing to support the molten weld metal. Without backing bars. (e) Copper backing bars are useful when welding thin steel. (a) There are a large number of variations to the process that give submerged arc welding additional capabilities. Some of the more popular variations are: 1. 2. Strip electrode for surfacing.(d) One side welding with complete root penetration can be obtained with submerged arc welding. Three-wire systems--separate power source.

individual wire feeders must be used to provide electrical insulation between the two electrodes.
. When two power sources are used. When two dc arcs are in close proximity.
(c) The two-wire tandem electrode position with individual power sources is used where extreme penetration is required. When a single-power source is used. They can also be placed one in front of the other in the tandem electrode position. The electrodes can be placed side by side. The first electrode creates a digging action and the second electrode fills the weld joint.(b) The multi-wire systems offer advantages since deposition rates and travel speeds can be improved by using more electrodes. the same drive rolls are used for feeding both electrodes into the weld. This is called transverse electrode position. one with a single-power source and one with two power sources. With two electrodes and separate power. Figure 10-68 shows the two methods of utilizing two electrodes. The leading electrode is positive with the trailing electrode negative. it is possible to utilize different polarities on the two electrodes or to utilize alternating current on one and direct current on the other.

This increases deposition rates without decreasing weld metal properties. Extremely high currents can be used with correspondingly high travel speeds and deposition rates. When the width of the strip is over 2 in. A wide bead is produced that has a uniform and minimum penetration. It is used for overlaying the inside of vessels to provide the corrosion resistance of stainless steel while utilizing the strength and economy of the low-alloy steels for the wall thickness. In some cases. a magnetic arc oscillating device is used to provide for even burnoff of the strip and uniform penetration. the second electrode is connected to alternating current to avoid the interaction of the arc. This process variation is shown by figure 10-69. (d) The three-wire tandem system normally uses ac power on all three electrodes connected to three-phase power systems.
(f) Another way of increasing the deposition rate of submerged arc welding is to add iron base ingredients to the joint under the flux. (51 mm). (e) The strip welding system is used to overlay mild and alloy steels usually with stainless steel. Metal additives can also be used for special surfacing applications. The iron in this material will melt in the heat of the arc and will become part of the deposited weld metal.there is a tendency for arc interference between them. This variation can be
. A strip electrode feeder is required and special flux is normally used. These systems are used for making highspeed longitudinal seams for large-diameter pipe and for fabricated beams.

(2) Submerged arc welding flux shields the arc and the molten weld metal from the harmful effects of atmospheric oxygen and nitrogen. Each of these variations requires special engineering to ensure that the proper material is added to provide the desired deposit properties. As this molten flux cools to a
. boilers. nuclear reactors. It is used for welding flanges to the web. The submerged arc welding process is widely used in the manufacture of most heavy steel products. Flux also provides a means of introducing alloys into the weld metal.used with single-wire or multi-wire installations. Figure 10-70 shows the increased deposition rates attainable. Another use is in the fabrication of trusses and beams. By regulating the addition of the proper material. The heavy equipment industry is a major user of submerged arc welding.
(g) Another variation is the use of an electrically "cold" filler wire fed into the arc area. or for one of the multiple electrodes to introduce special alloys into the weld metal deposit. It is possible to utilize a flux-cored wire for the electrode. the properties of the deposited weld metal can be improved. etc. (1) Two materials are used in submerged arc welding: the welding flux and the consumable electrode wire. tanks. The flux contains deoxidizers and scavengers which help to remove impurities from the molten weld metal. (11) Typical applications. f. chemical vessels. These include pressure vessels. The "cold" filler rod can be solid or flux-cored to add special alloys to the weld metal. Materials Used.

The basic arrangement for a plasma arc cutting torch. The intensity and velocity of the arc plasma gas are determined by such variables as the type of orifice gas and its entrance pressure. and cutting with water added. so it can be recovered and reused. the slag will actually peel without requiring special effort for removal. uses a maximum of 100 amperes and a much smaller torch than the high current version. it forms a covering which protects the surface of the weld.
Section III. In this way. The unmelted portion of the flux does not change its form and its properties are not affected. As the orifice gas passes through the arc. and the plasma energy density on the work. Table 10-24 shows the flux wire combination and the mechanical properties of the deposited weld metal. Low current arc cutting. high current plasma cutting. Many fluxes are not marked for size of particles because the size is designed and produced for the intended application. it is heated rapidly to a high temperature. This is covered by the American Welding Society Standard. which produces high-quality cuts of thin materials. RELATED PROCESSES
10-15. Submerged arc fluxes come in different particle sizes. expands and accelerates as it passes through the constricting orifice. General. similar to the plasma arc welding torch. This is easily done after the weld has cooled.glassy slag.
. In groove welds. Bare carbon steel electrodes and fluxes for submerged arc welding. In many cases. is by means of the deposited weld metal produced by various combinations of electrodes and proprietary submerged arc fluxes. the solidified slag may have to be removed by a chipping hammer. Three variations of the process exist: low current plasma cutting. The plasma arc cutting process cuts metal by melting a section of metal with a constricted arc. The flux that does melt and forms the slag covering must be removed from the weld bead. A method of classifying fluxes. however. (4) There is no specification for submerged arc fluxes in use in North America. is shown in figure 10-71. A high velocity jet flow of hot ionized gas melts the metal and then removes the molten material to form a kerf. All plasma torches constrict the arc by passing it through an orifice as it travels away from the electrode toward the workpiece. fluxes can be designated to be used with different electrodes to provide the deposited weld metal analysis that is desired. (3) Fluxes are designed for specific applications and for specific types of weld deposits. PLASMA ARC CUTTING (PAC) a. Modifications of processes and equipment have been developed to permit use of oxygen in the orifice gas to allow efficient cutting of steel. constricting orifice shape and diameter.

Torch designs for introducing shielding gas or water around the plasma flame are available. and a supply of clean cooling water. The electrode and nozzle are water cooled to prolong their lives. Both single and multiple port nozzles may be used for PAC. Equipment. one or more cutting gases. However. a power supply. Mechanized PAC torches are mounted on shape cutting machines similar to mechanized oxyfuel gas shape cutting equipment. numerical control. a control unit. larger diameters are required at higher currents. Controls for high-power automatic PAC may also contain programning features for upslope and downslope of current and orifice gas flow. or computer. and the cutting speed range. A cutting torch consists of an electrode holder which centers the electrode tip with respect to the orifice in the constricting nozzle. Control consoles for PAC may contain solenoid valves to turn gases and cooling water on and off. Multiple port nozzles have auxiliary gas ports arranged in a circle around the main orifice. the type and thickness of the work metal. (1) Cutting torch. Power sources for PAC are specially designed units with open-circuit voltages in the range of 120 to 400 V.
. (3) Power sources. They usually have flowmeters for the various types of cutting gases used and a water flow switch to stop the operation if cooling water flow falls below a safe limit. PAC torches are similar in appearance to gas tungsten arc welding electrode holders. Equipment is available for both manual and mechanized PAC. Nozzle design depends on the type of PAC and the metal being cut. Cutting may be controlled by photoelectric tracing. These nozzles produce better quality cuts than single port nozzles at equivalent travel speeds. cut quality decreases with increasing travel speed. Orifice diameter depends on the cutting current. Plasma arc cutting requires a torch. (2) Controls. Nozzles with various orifice diameters are available for each type of torch. both manual and machine types. Plasma gas is injected into the torch around the electrode and exits through the nozzle orifice. All of the arc plasma passes through the main orifice with a high gas flew rate per unit area.b. A power source is selected on the basis of the design of PAC torch to be used. Their volt-ampere output characteristic must be the typical drooping type.

nitrogenhydrogen mixtures.(a) Heavy cutting requires high open-circuit voltage (400 V) for capability of piercing material as thick as 2 in. nitrogen is used for the plasma gas with carbon dioxide (C02) for shielding.
. (b) The output current requirements range from about 70 to 1000 A depending on the material. manual cutting equipment uses lower open-circuit voltages (120 to 200 V). Some systems use nitrogen for the plasma forming gas with oxygen injected into the plasma downstream of the electrode. straight polarity (dcsp). This forms a low resistance path to ignite the main arc between the electrode and the workpiece. (4) Gas selection. its thickness. The nozzle is connected to ground (positive) through a current limiting resistor and a pilot arc relay contact. (c) For some nonferrous cutting with the dual flow system. or argon-hydrogen mixtures. The process operates on direct current. the pilot arc relay may be opened automatically to avoid unnecessary heating of the constricting nozzle. Titanium and zirconium are cut with pure argon because of their susceptibility to embrittlement by reactive gases. argon-hydrogen plasma gas and nitrogen shielding are used. The unit may also contain the pilot arc and high frequency power source circuitry. an arc is struck between the electrode in the torch and the workpiece. When the main arc ignites. This arrangement prolongs the life of the electrode by not exposing it to oxygen. The arc is initiated by a pilot arc between the electrode and the constricting nozzle. Low current. 20 percent 02) or nitrogen for plasma gas. For better quality cuts. electrode negative. The welding power supply then maintains this low current arc inside the torch. Ionized orifice gas from the pilot arc is blown through the constricting nozzle orifice. c. and cutting speed. In the transferred arc mode. (51 mm). The pilot arc is initiated by a high frequency generator connected to the electrode and nozzle. Principles of Operation. Some power sources have the connections necessary to change the open-circuit voltage as required for specific applications. with a constricted transferred arc. (1) The basic plasma arc cutting circuitry is shown in figure 10-72. Most nonferrous metals are cut by using nitrogen. (a) Cutting gas selection depends on the material being cut and the cut surface quality requirements. (b) Carbon steels are cut by using compressed air (80 percent N2. Nitrogen is used with the water injection method of PAC.

Auxiliary shielding. it may be carbon dioxide (CO2) or air.(2) Because the plasma constricting nozzle is exposed to the high plasma flare temperatures (estimated at 18. the torch should be de-signed to produce a boundary layer of gas between the plasma and the nozzle. The usual orifice gas is nitrogen. They are generally applicable to materials in the 1/8 to 1-1/2 in. Dual flow plasma cutting provides a secondary gas blanket around the arc plasma. but the cut quality is not satisfactory for many applications.
.232°F (10. (3) Several process variations are used to improve the PAC quality for particular applications. In addition. (a) Dual flow plasma cutting. For mild steel. For mild steel. is used to improve cutting quality. CO2. cutting speeds are slightly faster than with conventional PAC. in the form of gas or water. (3 to 38 mm) thickness range. and an argonhydrogen mixture for aluminum. for stainless steals. The shielding gas is selected for the material to be cut.032 to 25. the nozzle must be made of water-cooled copper. as shown in figure 10-73.000°C)).000 to 14.

it cools the kerf edge. the plasma gas swirls as it emerges from the nozzle and water jet. (c) Water injection plasma cutting. Water is used in place of the auxiliary shielding gas. When the orifice gas and water are injected in tangent. Because most of the water leaves the nozzle as a liquid spray. In shape cutting applications. The water constricted plasma produces a narrow. The water jet also shields the plasma from mixing with the surrounding atmosphere. the direction of travel must be selected to produce a perpendicular cut on the part and the bevel cut on the scrap. producing a sharp corner. sharply defined cut at speeds above those of conventional PAC. This modification of the PAC process uses a symmetrical impinging water jet near the constricting nozzle orifice to further constrict the plasma flame. This technique is similar to dual flow plasma cutting.
. The other side of the kerf is beveled. Cut appearance and nozzle life are improved by the use of water in place of gas for auxiliary shielding.(b) Water shield plasma cutting. This can produce a high quality perpendicular face on one side of the kerf. The end of the nozzle can be made of ceramic. The kerf is clean. The arrangement is shown in figure 10-74. which helps to prevent double arcing. Cut squareness and cutting speed are not significantly improved over conventional PAC.

plate beveling. if sufficiently high travel speed is attainable. the torch is mounted on a mechanical carriage. (7) Special controls are required to adjust both plasma and secondary gas flow. (8) Plasma cutting torches will fit torch holders in automatic flame cutting machines. Most applications are for carbon steel. Plasma arc cutting can be used to cut any metal. This will help reduce the amount of fumes released into the air. Automatic shape cutting can be done with the same equipment used for oxygen cutting.
. which includes a circulating pump and a heat exchanger. and nickel alloys. The cutting torch is of special design for cutting and is not used for welding. d. (6) The metals usually cut with this process are the aluminums and stainless steels. shape cutting. It can also be used for piercing holes and for gouging.(4) For high current cutting. Cutting should be done over a water reservoir so that the particles removed from the cut will fall in the water. copper alloys. (5) The plasma arc cutting torch can be used in all positions. (9) The amount of gases and tines generated requires the use of local exhaust for proper ventilation. Work tables containing water which is in contact with the underside of the metal being cut will also reduce noise and smoke. Applications. The cooling system should be self-contained. aluminum. A water spray is used surrounding the plasma to reduce smoke and noise. and piercing. and stainless steel. The process can also be used for cutting carbon steels. Torchcooling water is required and is monitored by pressure or flow switches for torch protection. It can be used for stack cutting.

(1) The circuit diagram for air carbon arc cutting or gouging is shown by figure 10-76. Equipment. This involves protective clothing. AIR CARBON ARC CUTTING (AAC) a. 9 filter glass lens. Air carbon arc cutting and metal removal differ from plasma arc cutting in that they employ an open (unconstricted) arc. Air carbon arc cutting is an arc cutting process in which metals to be cut are melted by the heat of a carbon arc. including the cutting of stainless and aluminum for production and maintenance. It strikes the molten metal immediately behind the arc. The normal protective clothing to protect the cutter from the arc must also be worn. gloves. The cutter must wear ear protection. which is independent of the gas jet. The air carbon arc process is shown in figure 10-75. precautions must be taken to operate it within its rated output of current and duty cycle. (1) The noise level generated by the high-powered equipment is uncomfortable. and helmet. AC type carbon electrodes must be used. 10-16. General. The air jet is external to the consumable carbongraphite electrode. The molten metal is removed by a blast of air.WARNING Ear protection must be worn when working with high-powered equipment. This is a method for cutting or removing metal by melting it with an electric arc and then blowing away the molten metal with a high velocity jet of compressed air. When using a CV power source. Constant voltage can be used with this process. Low current plasma gouging can also be used for upgrading castings. The helmet should be equipped with a shade no. (2) There are many applications for low-current plasma arc cutting. Plasma cutting can also be used for stack cutting and it is more efficient than stack cutting with the oxyacetylene torch. Normally.
. Alternating current power sources having conventional drooping characteristics can also be used for special applications. conventional welding machines with constant current are used.
b.

Special heavy duty high current machines have been made specifically for the air carbon arc process. The holder includes a small circular grip head which contains the air jets to direct compressed air along the electrode. (3) The electrode holder is designed for the air carbon arc process. This head can be rotated to allow different angles of electrode with respect to the holder.5 liter per min) up to 50 cu ft per min (24 liter per min) for the largest-size carbon electrodes. This is because of extremely high currents used for the large size carbon electrodes. The volume of compressed air required ranges from as low as 5 cu ft per min (2. Holders are available in several sizes depending on the duty cycle of the work performed. water-cooled holders are used. A valve is included in the holder for turning the compressed air on and off. (4) The air pressure is not critical but should range from 80 to 100 psi (552 to 690 kPa). It will require up to a ten-horsepower compressor when using the largest-size electrodes. A heavy electrical lead and an air supply hose are connected to the holder through a terminal block. and size of carbon electrode used. the welding current.(2) Equipment required is shown by the block diagram. A one-horsepower compressor will supply sufficient air for smaller-size electrodes. It also has a groove for gripping the electrode.
. For extra heavy duty work.

6 in.
c. and to prepare grooves for welding. the dc type and the ac type. and allow continuous operation. and starts easier. for root gouging of full penetration welds. the electrode is operated with the electrode positive. Table 10-25 shows the electrode types and the arc current range for different sizes. (2) The air carbon arc cutting and gouging process is normally manually operated. (a) The plain uncoated electrode is less expensive. It lasts longer and carries higher current. Advantages and Major Uses. (300 mm) long. (1) The air carbon arc cutting process is used to cut metal. The dc type is more common.0 to 25.4 mm). to gouge out defective metal. carries less current. (b) The copper-coated electrode provides better electrical conductivity between it and the holder. since the metal is melted and removed quickly. Air carbon arc cutting is used when slightly ragged edges are not objectionable. For normal use. This is considered machine cutting or
. The composition ratio of the carbon and graphite is slightly different for these two types. Electrodes come in several types. This reduces the tendency towards distortion and cracking.(5) The carbon graphite electrodes are made of a mixture of carbon and graphite plus a binder which is baked to produce a homogeneous structure. The ac type contains special elements to stabilize the arc. The apparatus can be mounted on a travel carriage. The copper-coated electrode is better for maintaining the original diameter during operation. The area of the cut is small and. It is used for direct current electrode negative when cutting cast irons. however. Electrodes range in diameter from 5/32 to 1 in. to remove old or inferior welds. Coppercoated electrodes are of two types. Electrodes are normally 12 in. (4. the surrounding area does not reach high temperatures. (150 mm) electrodes are available Copper-coated electrodes with tapered socket joints are available for automatic operation.

(5) The process is not recommended for weld preparation for stainless steel. (3) The air carbon arc cutting process can be used in all positions. Special applications have been made where cylindrical work has been placed on a lathe-like device and rotated under the air carbon arc torch. and other similar metals without subsequent cleaning. zirconium. Process Principles. usually by grinding. d. (4) The air carbon arc process can be used for cutting or gouging most of the common metals. magnesium. titanium. must remove all of the surface carbonized material adjacent to the cut. Use in the overhead position requires a high degree of skill. It can also be used for gouging in all positions.
. This cleaning. This is machine or automatic cutting. The process can be used to cut these materials for scrap for remelting. (1) The procedure schedule for making grooves in steel is shown in table 10-26 below. and carbon and stainless steels.gouging. depending on operator involvement. iron. copper. Metals include: aluminums.

the air blast will cause the molten metal to travel a very long distance.(2) To make a cut or a gouging operation. First. two other precautions must be observed. The speed of travel. All
. the cutter strikes an arc and al-most immediately starts the air flow. Electrode diameter determines the groove width. (3) The normal safety precautions similar to carbon arc welding and shielded metal arc welding apply to air carbon arc cutting and gouging. and the electrode size and current determine the groove depth. However. Metal deflection plates should be placed in front of the gouging operation. the electrode angle. The electrode is pointed in the direction of travel with a push angle approximately 45° with the axis-of the groove.

Resistance spot welding. and after the current flow forces the heated parts together so that coalescence will occur. RESISTANCE WELDING a. These are flash welding. and upset welding. preparing joints. the mass of molten metal removed is quite large and will become a fire hazard if not properly contained. The force applied before. Three factors involved in making a resistance weld are the amount of current that passes through the work. and the time the current flows through the work. b. (2) This concept of resistance welding is most easily understood by relating it to resistance spot welding. projection welding. ear muffs or ear plugs should be worn by the arc cutter. (5) The process is widely used for back gouging. Ear protection. is shown by figure 10-77. the pressure that the electrodes transfer to the work. Principles of the Process. resistance seam welding. There are at least seven important resistance-welding processes. At high currents with high air pressure a very loud noise occurs. resistance spot welding. At high-current levels. (1) The resistance welding processes differ from all those previously mentioned. Resistance welding is a group of welding processes in which coalescence is produced by the heat obtained from resistance of the work to electric current in a circuit of which the work is a part and by the application of pressure. during.
. percussion welding. Pressure is required throughout the entire welding cycle to assure a continuous electrical circuit through the work. General. High current at a low voltage flows through the circuit and is in accordance with Ohm’s law.combustible materials should be moved away from the work area. (4) The second factor is the high noise level. the most popular. and removing defective weld metal. Filler metal is rarely used and fluxes are not employed. 10-17. Heat is generated by the passage of electrical current through a resistance circuit. high frequency resistance welding.

It is an advantage to shorten welding tire.(a) I is the current in amperes. the actual resistance welding formula is H (heat energy) =I2 x R x T x K (c) In this formula. the heat generated is quadrupled.
. the electrodes are water cooled to minimize the heat generated between the electrode and the work. The total energy is expressed by the formula: Energy equals I x E x T in which T is the time in seconds during which current flows in the circuit. (4) Heat is also generated at the contact between the welding electrodes and the work. therefore. In most applications. T is the time of current flow in seconds. I = current squared in amperes. For practical reasons a factor which relates to heat losses should be included. This amount of heat generated is lower since the resistance between high conductivity electrode material and the normally employed mild steel is less than that between two pieces of mild steel. The heat losses should be held to a minimum. and K represents the heat losses through radiation and conduction. (3) Welding heat is proportional to the square of the welding current. the time can be reduced considerably. thus. and R is the resistance of the material in ohms. Mechanical pressure which forces the parts together helps refine the grain structure of the weld. E is the voltage in volts. (b) Combining these two equations gives H (heat energy) = 12 x R x T. If the current is doubled. R is the resistance of the work in ohms. if current is doubled. Welding heat is proportional to the total time of current flow. The welding heat generated is directly proportional to the resistance and is related to the material being welded and the pressure applied.

and movement. Welding is performed with operators who normally load and unload the welding machine and operate the switch for initiating the weld operation. Some metals require heat treatment after welding for satisfactory mechanical properties. The pressure is applied by mechanical. In view of this. and joint design are related to specific resistance welding processes. or pneumatic systems. c. Resistance welding has the advantage of producing a high volume of work at high speeds and does not require filler materials.(5) Resistance welds are made very quickly. Difficulties may be encountered when welding certain metals in thicker sections. Resistance welding equipment utilizes programmers for controlling current. when it is involved. Welding programs for resistance welding can become quite complex. the thicknesses that can be welded. Weldable Metals. (1) Metals that are weldable. time cycles. quality welds do not depend on welding operator skill but more on the proper set up and adjustment of the equipment and adherence to weld schedules. tubing and smaller structural sections. (6) Resistance welding operations are automatic. particularly in the welding of thinner material. (8) The position of making resistance welds is not a factor. each process has its own time cycle. The automotive industry is the major user of the resistance welding processes. (7) Resistance welding is used primarily in the mass production industries where long production runs and consistent conditions can be maintained.
. Resistance welding is also used in the steel industry for manufacturing pipe. however. Most of the common metals can be welded by many of the resistance welding processes (see table 10-27). Resistance welds are reproducible and high-quality welds are normal. Motion. Current control is completely automatic once the welding operator initiates the weld. followed by the appliance industry. pressure. Resistance welding is used by many industries manufacturing a variety of products made of thinner gauge metals. is ap-plied mechanically. hydraulic.

General. After a predetermined time. weldability becomes fair. Heat is generated by the flashing and is localized in the area between the two parts. The fourth group is the refractory metals. Current flow is possible because of the light contact between the two parts being flash welded.(2) Weldability is controlled by three factors: resistivity. Above 2. thermal conductivity. there is an intense flashing arc and heating of the metal on the surfaces abutting each other. Flashing and upsetting are accompanied by expulsion of metal from the joint. and melting temperature. Between 0. and Kt is the relative thermal conductivity with copper equal to 1. In this formula. As soon as this material is flashed away.0.
. which have extremely high melting points and are more difficult to weld. and by the application of pressure after heating is substantially completed. R is resistivity. mild steel would have a weldability rating of over 10. Ferrous metals all fall into this category. (4) These three properties can be combined into a formula which will provide an indication of the ease of welding a metal. This is shown by figure 10-78. The arcs are extinguished and upsetting occurs. This formula is:
In this formula. it is a poor rating. (1) Flash welding is a resistance welding process which produces coalescence simultaneously over the entire area of abutting surfaces by the heat obtained from resistance to electric current between the two surfaces.25. W equals weldability. Pressure is then applied. These are difficult to weld because of very high thermal conductivity. The precious metals comprise the third group.25 and 0. 10-18. The surfaces are brought to the melting point and expelled through the abutting area. (3) Metals with a high resistance to current flow and with a low thermal conductivity and a relatively low melting temperature would be easily weldable. Metals that have a lower resistivity but a higher thermal conductivity will be slightly more difficult to weld.0 weldability is excellent.00. During the welding operation. another small arc is formed which continues until the entire abutting surfaces are at the melting temperature. the two pieces are forced together and joining occurs at the interface. FLASH WELDING (FW) a. If W is between 0. If weldability (W) is below 0. Aluminum has a weldability factor of from 1 to 2 depending on the alloy and these are considered having a good weldability rating. and F is the melting temperature of the metal in degrees C. weldability is good. aluminum and magnesium. This includes the light metals. Copper and certain brasses have a low weldability factor and are known to be very difficult to weld.75.75 and 2.

of cross section of the weld. It can be from 1/8 in. upset pressures are increased. The joints must be cut square to provide an even flash across the entire surface. The weld may not be uniform across the entire cross section. and fatigue and impact strength will be reduced. (3. a porous low strength weld will result.2 mm) for thin material up to several inches for heavy material. cross section at 8 seconds. rust. The lowest voltage is normally 2 to 5 volts per square in. For high-strength materials. or the time between the end of flashing period and the end of the upset period. and grease must be removed. In the flash welding operation. It is desirable to use the lowest flashing voltage at a desired flashing speed. If insufficient upset pressure is used. The design of the cam is related to the size of the parts being welded. these pressures may be doubled. For tubing or hollow members. The distance between the jaws after welding compared to the distance before welding is known as the burnoff. It requires a
. the pressures are reduced. The upset pressure for steel exceeds 10.(2) Flash welding can be used on most metals. No special preparation is required except that heavy scale. The speed of upset. (3) The upsetting force is usually accomplished by means of mechanical cam action. As the weld area is more compact. Excess upset pressure will result in expelling too much weld metal and upsetting cold metal. a certain amount of material is flashed or burned away. should be extremely short to minimize oxidation of the molten surfaces. The material to be welded is clamped in the jaws of the flash welding machine with a high clamping pressure. Welding currents are high and are related to the following: 50 kva per square in. 950 kPa). Flash welding is completely automatic and is an excellent process for mass-produced parts.000 psi (68.

The motor is disengaged from the flywheel and the other part to be welded is brought in contact under pressure with the rotating piece. rotational notion ceases. offer the same welding advantages. When the rotating piece stops. A flywheel is revolved by a motor until a preset speed is reached. General. (a) In the original process. Additional pressure is applied and coalescence occurs. During the predetermined time during which the rotational speed of the part is reduced. FRICTION WELDING (FRW) a. When a suitable high temperature has keen reached. in turn. Additional pressure is provided to complete the weld. rotates one of the pieces to be welded. the weld is completed. pressure. (b) The other variation is inertia welding. Slightly better control is claimed with the original process. This process can be accurately controlled when speed. It. The two parts are brought in contact under pressure for a specified period of time with a specific pressure.
. the flywheel is brought to an immediate stop. and are shown by figure 10-79. The work parts are held together under pressure. (2) There are two variations of the friction welding process.machine of large capacity designed specifically for the parts to be welded. and time are closely regulated. (c) Both methods utilize frictional heat and produce welds of similar quality. (1) Friction welding is a solid state welding process which produces coalescence of materials by the heat obtained from mechanically-induced sliding motion between rubbing surfaces. Rotating power is disengaged from the rotating piece and the pressure is increased. This process usually involves the rotating of one part against another to generate frictional heat at the junction. Flash welds produce a fin around the periphery of the weld which is normally removed. They are described below. 10-19. one part is held stationary and the other part is rotated by a motor which maintains an essentially constant rotational speed. The two methods are similar.

(2) No filler metal is required and flux is not used. Advantages. (1) Friction welding can produce high quality welds in a short cycle time.b.
.

which occurs around the outside perimeter of the weld. (1) Electron beam welding (EBW) is a welding process which produces coalescence of metals with heat from a concentrated beam of high velocity electrons striking the surfaces to be joined. c.
.(3) The process is capable of welding most of the common metals. (1) There are three important factors involved in making a friction weld: (a) The rotational speed which is related to the material to be welded and the diameter of the weld at the interface. Pressure changes during the weld sequence. (b) If the flash curls too far back on the outside diameter. Visual inspection of weld quality can be based on the flash. It can also be used to join many combinations of dissimilar metals. The flash is normally removed after welding. of the electrons is transformed into heat upon impact. the pressure was too low. Process Principles. but is increased to create the frictional heat. Heat is generated in the workpiece as it is bombarded by a dense stream of high-velocity electrons. Friction welding requires relatively expensive apparatus similar to a machine tool. (c) Between these extremes is the correct flash shape. Virtually all of the kinetic energy. or the energy of motion. It is normally a matter of a few seconds. one of the parts to be welded is round in cross section. which can be set according to the weld schedule established for the parts to be joined. (a) If the flash sticks out relatively straight from the joint. ELECTRON BEAM WELDING a. The actual operation of the machine is automatic. pressure is rapidly increased so forging takes place immediately before or after rotation is stopped. or the speed too high. it indicates that the time was too long and the pressure was too high. it indicates that the welding time was was too short. 10-20. These joints may crack. This flash will usually extend beyond the outside diameter of the parts and will curl around back toward the part but will have the joint extending beyond the outside diameter of the part. This is not an absolute necessity. When the rotation is stopped. (b) The pressure between the two parts to be welded. pressure is very low. (2) Normally for friction welding. It is controlled by a sequence controller. At the start. General. (c) The welding time is related to the shape and the type of metal and the surface area.

and the high voltage system with accelerating voltages in the 100.000-volt (30 kv) to 60. In both systems. the electron gun and the workpiece are housed in a vacuum chamber. Figure 10-80 shows the principles of the electron beam welding process. the beam of electrons is focused on a tar-get of either tungsten or molybdenum which gives off X-rays. Magnetic focusing coils located beyond the anode focus and deflect the electron beam.000-volt (60 kv) range. the power supply with controls. accelerates the beam of electrons.
. (1) There are three basic components in an electron beam welding machine. Equipment. In electron beam welding.000-volt (100 kv) range. The power supply furnishes both the filament current and the accelerating voltage. The higher voltage system emits more X-rays than the lower voltage system. and focuses it on the workpiece. which uses accelerating voltages in 30.(2) Two basic designs of this process are: the low-voltage electron beam system. (3) In the electron beam welding machine. These are the electron beam gun. the target is the base metal which absorbs the heat to bring it to the molten stage. X-rays may be produced if the electrical potential is sufficiently high. the electron beam is focused on the workpiece at the point of welding. In welding. The electrons are emitted by a heated cathode or filament and accelerated by an anode which is a positively-charged plate with a hole through which the electron beam passes.
b. The electron beam gun is similar to that used in a television picture tube. and a vacuum work chamber with work-handling equipment. Both can be changed to provide different power input to the weld. The target becomes extremely hot and must be water cooled. (2) The electron beam gun emits electrons. In an X-ray tube.

This occurs when the highly accelerated electron hits the base metal. This creates metal vapors but the electron beam travels through the vapor much easier than solid metal. however. the electron gun is in its own separate chamber separate from the work chamber by a small orifice through which the electron beam travels.4 mm) thick while in the medium vacuum the thickness that can be welded is reduced to 2. the heat affected zone is much smaller than that of any arc welding process. The width of the penetration pattern is extremely narrow. The thickness that can be welded in a high vacuum is up to 6.995 percent argon. and certain insulating varnishes in electric rotors may volatilize in a vacuum. (1) Recent advances in equipment allow the work chamber to operate at a medium vacuum or pressure. This causes the beam to penetrate deeper into the base metal. the rotor and gearboxes are located outside the vacuum chamber with shafts operating through sealed bearings. (3) In a high vacuum system. In addition. The cooling rate is much higher and for many metals this is advantageous. the working distance is reduced to 12. (152. connected to the chamber containing the electron gun.8 mm). Since the electron beam has tremendous penetrating characteristics.0 in. It is evacuated by means of mechanical pumps and diffusion pumps to reduce the pressure to a high vacuum. The depth-to-width can exceed a ratio of 20 to 1. lubricants. In the medium vacuum mode. penetration is increased. (2) Electron beam welding was initially done in a vacuum because the electron beam is easily deflected by air.
. for high carbon steel this is a disadvantage and cracking may occur. (50. pump down time is reduced. because of the almost parallel sides of the weld nugget. (762.0 in. The addition of the heat brings about a substantial temperature increase at the point of impact. One of the major advantages of electron beam welding is its tremendous penetration. This is based on the same electron gun and power in both cases. The electrons in the beam collide with the molecules of the air and lose velocity and direction so that welding can not be performed.0 in.0 in. The succession of electrons striking the same place causes melting and then evaporation of the base metal. (304. Mechanical pumps can produce vacuums to the medium pressure level. The travel mechanisms must be designed for vacuum installations since normal greases.0 mm) away from the workpiece. Work-handling equipment is required to move the workpiece under the electron beam and to manipulate it as required to make the weld. c. the electron beam can be located as far as 30. As the power density is increased. In this system. In the medium vacuum. Process Principles. It will penetrate slightly below the surface and at that point release the bulk of its kinetic energy which turns to heat energy. With the medium vacuum. A diffusion vacuum pump is run continuously. It is sometimes called a "soft" vacuum This vacuum range allowed the same contamination that would be obtained in atmosphere of 99. d. with the lower heat input. The vacuum can be obtained by using mechanical pumps only. distortion is very greatly minimized. Heretically sealed motors and sealed gearboxes must be used.(4) The vacuum work chamber must be an absolutely airtight container.8 mm). the vacuum in the work chamber is not as high. In some cases. so that it will operate efficiently. Advantages.

The other variable. The electron beam gun is housed in a high vacuum chamber. the beam currents can be as low as 25 milliamperes. The maximum thickness that can be welded currently is approximately 2 in. The power in an electron beam weld compared with a gas metal arc weld would be in the same relative amount. however the workpiece must be positional with 11/2 in. is related to the focus of the beam. The electron beam current ranges from 250 to 1000 milliamperes. The gas metal arc weld would require higher power to produce the same depth of penetration. When the beam is focused at the surface. penetration is reduced. The other parameter that must be controlled is the gun-to-work distance. (5) The heat input of electron beam welding is controlled by four variables: (a) Number of electrons per second hitting the workpiece or beam current. travel speed. (51 mm). Each of these intermediate stages is reduced in pressure by means of vacuum pumps. the work area is maintained at atmospheric pressure during welding. there will be more reinforcement on the surface. (d) Speed of travel or the welding speed. As beam current is increased. there will be excessive reinforcement and the width of the weld will be greater. The electron beam passes from one chamber to another through a small orifice large enough for the electron beam but too small for a large volume of air. In this system. The third factor. (7) The beam spot size can be varied by the location of the fecal point with respect to the surface of the part. As it is increased in depth below the surface. penetration is increased. (38 mm) of the beam exit nozzle. The accelerating voltage is within the two ranges mentioned previously. The nonvacuum system utilizes the highvoltage power supply. deeper penetration will result. a high vacuum is maintained in the electron beam gun chamber. (c) Diameter of the beam at or within the workpiece. are used in establishing welding parameters. the beam spot size. The nonvacuum system can thus be used for the largest weldments. (b) Electron speed at the moment of impact. the accelerating potential. By means of these differential pressure chambers. (6) The first two variables in (5). beam current and accelerating potential. the beam spot size. (8) Penetration is also dependent on the beam current. also affects penetration. There are several intermediate chambers between the gun and the atmospheric work area. When the beam is focused above the surface.(4) The most recent development is the nonvacuum electron beam welding system. As travel speed is increased. Travel speeds can be extremely high and relate to the thickness of the base metal. Penetration can be increased by placing the fecal point below the surface of the base metal. and the fourth factor is also part of the procedure. The energy in joules per inch for
. (9) The heat input produced by electron beam welds is relatively small compared to the arc welding processes.

Many combinations of dissimilar metals can also be welded. The major problem is the welding of plain carbon steel which tends to become porous when welded in a vacuum.7 mm) thick stainless steel would only be 0. It is also used to a very great degree in the automatic energy industry for remote welding and for welding the refractory metals.the electron beam weld may be only 1/10 as great as the gas metal arc weld. (10) The weld joint details for electron beam welding must be selected with care. parts can be brought into and taken out of the vacuum work chamber by means of interlocks so that the process can be made more or less continuous.
. there are still the possibilities of defects of welds in this process as with any other. This helps deoxidize the molten metal and produce dense welds. e. One of the most productive applications is the welding of automotive catalytic converters around the entire periphery of the converter. The metals that are most often welded are the super alloys. the reactive metals. (12) The non-vacuum system is finding acceptance for other applications. The width of a weld in 1/2 in. Weldable Metals. The melting of the metal releases gases originally in the metal and results in a porous weld. it has to be designed specifically for the job at hand. when welding mild steel highly deoxidized filler metal is sometimes used. Welds are extremely narrow. In other versions of the medium vacuum system. Small misalignment would cause the electron beam to completely miss the weld joint. Newer systems are available where the chamber is sealed around the part to be welded.00 mm). the refractory metals. ordinary lap joints are used and the weld is an arc seam type of weld. In high vacuum chamber welding. special techniques must be used to properly align the electron beam with the joint. filler metal is not used in electron beam welding. If deoxidizers cannot be used. This can be done since the distortion is minimal. the process is not suitable. however. (11) In the case of the medium vacuum system. Welding joint details normally used with gas tungsten arc welding can be used with electron beam welding. much larger work chambers can be used. Electron beam welding is not a cure-all. The automotive industry is using this system for welding gear clusters and other small assemblies of completely machined parts. The latest uses a sliding seal and a movable electron beam gun. The power density is in the range of 100 to 10. and the stainless steels. The electron beam is not visible in the vacuum. Normally. (13) The electron beam process is becoming increasingly popular where the cost of equipment can be justified over the production of many parts. The electron beam weld is equivalent to the SMAW weld with less power because of the penetration obtainable by electron beam welding. (1.04 in. Where joint fitup is not precise. The depth to width ratio allows for special lap type joints. In this case. Preparation for welding must be extremely accurate. Almost all metals can be welded with the electron beam welding process. (12. Special optical systems are used which allow the operator to align the work with the electron beam.000 kw/in2.

the electromagnetic radiation impinges on the surface of the base metal with such a concentration of energy that the temperature of the
. Welding with Lasers.10-21. The gas lasers are pumped by high radio frequency generators which raise the gas atoms to sufficiently high energy level to cause lasing. General. A 6-kw laser is being used for automotive welding applications and a 10-kw laser has been built for research purposes. It can be used in air. however. The spot can be made as small as 0.003 in. however. (1) Laser beam welding (LBW) is a welding process which produces coalescence of materials with the heat obtained from the application of a concentrate coherent light beam impinging upon the surfaces to be joined. there are only a few lasers in actual production use today. (2) The focused laser beam has the highest energy concentration of any known source of energy.076 mm) to large areas 10 times as big. Recent use of fiber optic techniques to carry the laser beam to the point of welding may greatly expand the use of lasers in metalworking. (5) The laser offers a source of concentrated energy for welding. The laser beam is a source of electromagnetic energy or light that can be pro jetted without diverging and can be concentrated to a precise spot. 2000-watt carbon dioxide laser systems are in use. (3) Gases can emit coherent radiation when contained in an optical resonant cavity. the continuous carbon dioxide laser now available with 100 watts to 10 kw of power seems the most promising for metalworking applications. It can operate at considerable distance from the workpiece. The large spot is used for heat treating. A sharply focused spot is used for welding and for cutting. The beam is coherent and of a single frequency. The high-powered laser is extremely expensive. (1) The laser can be compared to solar light beam for welding. LASER BEAM WELDING (LBW) a. Later developments allowed the gases in the laser to be cooled so that it could be operated continuously at higher power outputs. Currently. (0. The laser beam can be focused and directed by special optical lenses and mirrors. Higher powered systems are also being used for experimental and developmental work. (2) When using the laser beam for welding. Laser welding technology is still in its infancy so there will be improvements and the cost of equipment will be reduced. There are other types of lasers. b. Gas lasers can be operated continuously but originally only at low levels of power. The focused spot size is controlled by a choice of lenses and the distance from it to the base metal. (4) The coherent light emitted by the laser can be focused and reflected in the same way as a light beam.

Keyholing also minimizes the problem of beam reflection from the shiny molten metal surface since the keyhole behaves like a black body and absorbs the majority of the energy. high strength 1ow alloy steels. whether it is close or far away. that once the metal is raised to its melting temperature.0 mm) per minute. (5) The welding characteristics of the laser and of the electron beam are similar. and the heat-affected zones are much smaller. (254. inert gas is used to shield the molten metal from the atmosphere. This is compared to a current density of only 104 watts per square centimeter for arc welding. Weldable Metals. and titanium. keyholing occurs. however. The concentration of energy by both beams is similar with the laser having a power density in the order of 106 watts per square centimeter. when the power density rises above a certain threshold level. as with plasma arc welding. c.7 mm) thick are being welded at a speed of 10. Penetration is less when the beam is focused on the surface or deep within the surface. the surface conditions have little or no effect. (6) Laser beam welding has a tremendous temperature differential between the molten metal and the base metal immediately adjacent to the weld. (3) The distance from the optical cavity to the base metal has little effect on the laser. Laser welds made in these materials are similar in quality to welds made in the same materials by electron beam process. aluminum. One of the original questions concerning the use of the laser was the possibility of reflectivity of the metal so that the beam would be reflected rather than heat the base metal. (4) With laser welding. It was found.surface is melted vapor and melts the metal below.
. Maximum penetration occurs when the beam is focused slightly below the surface. The power density of the electron beam is only slightly greater. stainless steel. This provides for a high depth-to-width ratio. (7) Experimental work with the laser beam welding process indicates that the normal factors control the weld. Keyholing provides for extremely deep penetration. (12. Use of an inert gas jet directed along the metal surface eliminates the plasma buildup and shields the surface from the atmosphere. However. It can be focused to the proper spot size at the work with the same amount of energy available. Rapid cooling rates can create problems such as cracking in high carbon steels. In some applications.0 in. The laser beam has been used to weld carbon steels. As power is increased the depth of penetration is increased. Experimental work using filler metal is being used to weld metals that tend to show porosity when welded with either EB or LB welding. The laser beam is coherent and it diverges very little. The metal vapor that occurs may cause a breakdown of the shielding gas and creates a plasma in the region of high-beam intensity just above the metal surface. Materials 1/2 in. the molten meta1 takes on a radial configuration similar to convectional arc welding. Heating and cooling rates are much higher in laser beam welding than in arc welding. The plasma absorbs energy from the laser beam and can actually block the beam and reduce melting.

Thick section welds. by means of the flame produced at the tip of a welding torch. Upon cooling. WELDING PROCESSES AND TECHNIQUES
11-1. (3) OFW is ideally suited to the welding of thin sheet. OFW includes any welding operation that makes use of a fuel gas combined with oxygen as a heating medium. in which heat is obtained from the combustion of acetylene with air. (2) Weld bead size and shape and weld puddle viscosity are also controlled in the welding process because the filler metal is added independently of the welding heat source. if used. and small diameter pipe. tubes. b. (2) There are three major processes within this group: oxyacetylene welding. Advantages. (1) Oxyfuel gas welding (OEW) is a group of welding processes which join metals by heating with a fuel gas flame or flares with or without the application of pressure and with or without the use of filler metal. c. The process involves the melting of the base metal and a filler metal. Equipment. are not economical. and pressure gas welding. Welding with methylacetone-propadiene gas (MAPP gas) is also an oxyfuel procedure. oxyhydrogen welding. Fuel gas and oxygen are mixed in the proper proportions in a mixing chamber which may be part of the welding tip assembly. except for repair work. GENERAL GAS WELDING PROCDURES a. There is one process of minor industrial significance. Molten metal from the plate edges and filler metal.
. (1) One advantage of this welding process is the control a welder can exercise over the rate of heat input. General. the temperature of the weld zone. intermix in a common molten pool. and the oxidizing or reducing potential of the welding atmosphere. they coalesce to form a continuous piece.CHAPTER 11 OXYGEN FUEL GAS WELDING PROCEDURES
Section I. It is also used for repair welding. known as air acetylene welding. if used.

are necessary for stable operation and good heat transfer. This type of joint is limited to material under 3/16 in. and porosity in the weld. Thus. With relatively simple changes in equipment. Other gases. even at the higher ratios. Gases. and proprietary gases based on these. usually portable. (c) Adequate heat content. (2) The root opening for a given thickness of metal should permit the gap to be bridged without difficulty. d. postheating. Contaminants must be removed along the joint and sides of the base metal. fuel such as MAPP gas. yet it should be large enough to permit full penetration. (1) Commercial fuel gases have one common property: they all require oxygen to support combustion. propylene. preheating.(1) The equipment used in OFW is low in cost. and oxides can cause incomplete fusion. For thicknesses of 3/16 to 1/4 in. are used for oxygen cutting.8 mm) in thickness. These gas flames are excessively oxidizing at oxygen-tofuel gas ratios high enough to produce usable heat transfer rates. (1) Dirt. They are also used for torch brazing. (4. especially low alloy steels. The process is generally not used for welding refractory or reactive metals. Specifications for root openings should be followed exactly. Flame holding devices. These gases. manual and mechanized oxygen cutting operations can be performed. a
. Metals normally welded with the oxyfuel process include steels. natural gas. oil. must have the following: (a) High flame temperature. and torch brazing. (3) The thickness of the base metal at the joint determines the type of edge preparation for welding. braze welding. (2) Among the commercially available fuel gases. and many other operations where the demands upon the flame characteristics and heat transfer rates are not the same as those for welding. however. Thin sheet metal is easily melted completely by the flame. when burned with oxygen. a fuel gas. propane. Base Metal Preparation. and versatile enough to be used for a variety of related operations.8 to 6. have sufficiently high flame temperatures but exhibit low flame propagation rates. slag inclusions. (b) High rate of flame propagation. e. edges with square faces can be butted-together and welded. such as bending and straightening. acetylene most closely meets all these requirements. and most nonferrous metals. such as counterbores on the tips. (d) Minimum chemical reaction of the flame with base and filler metals. soldering. surface. (4. To be suitable for welding operations.4 mm).

too wide a root face. Beveling both sides reduces the amount of filler metal required by approximately one-half. or oxygen cut. This edge can be machined. (19 mm) and above are double beveled when welding can be done from both sides. (4) Joint edges 1/4 in. Beveled edges at the joint provide a groove for better penetration and fusion at the sides. ground. g. The welder can avoid oxides.
. Undercut or overlap at the sides of the welds can usually be detected by visual inspection. depending upon the application. Weld Quality. The root face can vary from 0 to 1/8 in. Gas consumption per unit length of weld is also reduced. Multiple layer welding is done by depositing filler metal in successive passes along the joint until it is filled.6 mm) wide is normal. (1) The appearance of a weld does not necessarily indicate its quality. the weld puddle is reduced in size. Multiple Layer Welding. which is equivalent to a variation in the included angle of the joint from 70 to 90 degrees.4 mm) and thicker should be beveled. because it is not detrimental to the welding operation or to the quality of the joint. but filler metal must be added to compensate for the opening. chipped. The final layer will not have this refinement unless an extra pass is added and removed or the torch is passed over the joint to bring the last deposit up to normalizing temperature.slight root opening or groove is necessary for complete penetration. The angle of bevel for oxyacetylene welding varies from 35 to 45 degrees. slag inclusions. The smaller puddle is more easily controlled. (5) A square groove edge preparation is the easiest to obtain. The thin oxide coating on oxygen-cut surface does not have to be removed. and incomplete fusion with the base metal. Plate thicknesses 3/4 in. (2) Grain refinement in the underlying passes as they are reheated increases ductility in the deposited steel. Visual examination of the underside of a weld will determine whether there is complete penetration or whether there are excessive globules of metal. (2) Oversized and undersized welds can be observed readily. (0 to 3. This procedure enables the welder to obtain complete joint penetration without excessive penetration and overheating while the first few passes are being deposited. or when several layers are required in welding thick metal. Weld gauges are available to determine whether a weld has excessive or insufficient reinforcement. (6. A bevel angle can be oxygen cut. f. Inadequate joint penetration may be due to insufficient beveling of the edges. (1) Multiple layer welding is used when maximum ductility of a steel weld in the aswelded or stress-relieved condition is desired. too great a welding speed. (1. Since the area covered with each pass is small. or poor torch and welding rod manipulation.2 mm). but feather edges are sometimes used. A root face 1/16 in.

are not suitable for welding ferrous materials due to their oxidizing characteristics. such as propane. such as incomplete fusion. (c) Tips should be used having flame-holding devices. h. When standard welding tips are used. This does not support combustion. the maximum flame velocity is so 1ow that it interferes seriously with heat transfer from the flame to the work. (d) Air contains approximately 80 percent nitrogen by volume. therefore. (2) Equipment.(3) Although other discontinuities. can be used to distribute and bum these gases. This makes it possible to use these fuel gases for many heating applications with excellent heat transfer efficiency. or gas or dirt inclusions. Special regulators may be obtained. excessive grain growth or the presence of hard spots cannot be determined visually. Porosity is a result of entrapped gases. which may be avoided by more careful flame manipulation and adequate fluxing where needed. with the exception of some manufactured city gases containing considerable amounts of hydrogen. Incomplete fusion may be caused by insufficient heating of the base metal. The total heat content is also lower. City gas and natural gas are supplied by pipelines. (a) Standard oxyacetylene equipment. usually carbon monoxide. with the exception of torch tips and regulators. (1) Principles of operation. butane. and holder flames. propane and butane are stored in cylinders or delivered in liquid form to storage tanks on the user's property. These gases are extensively used for brazing and soldering operations. These ratios produce highly oxidizing flames. (b) These fuel gases have relatively low flame propagation rates. produce lower flame temperatures than those burned with oxygen. utilizing both mechanized and manual methods. and cracking may or may not be apparent. Fuel gases burned with air. Welding With Other Fuel Gases. which prevent the satisfactory welding of most metals. The air-fuel gas flame is suitable only for welding light sections of lead and for light brazing and soldering operations. to permit higher gas velocities before they leave the tip. too rapid travel. and heating and cutting tips are available. counterbores. and natural gas. porosity. It is important to use tips designed for the fuel gas being employed. such as skirts. Hard spots and cracking are a result of metallurgical characteristics of the weldment.
. The highest flame temperatures of the gases are obtained at high oxygen-to-fuel gas ratios. city gas. many nonferrous and ferrous metals can be braze welded with care taken in the adjustment of flare and the use of flux. (a) Hydrocarbon gases. In some instances.

(c) The plumbing. The relation between the tip number and the diameter of the orifice may vary with different manufacturers. fuel gas usually is supplied from a small cylinder that is easily transportable. The fuel gas flows through the torch at a supply pressure of 2 to 40 psig and serves to aspirate the air.
. WORKING PRESSURES FOR WELDING OPERATIONS The required working pressure increases as the tip orifice increases. the joints in copper pipelines. For light work. and light brazing jobs. (6. see tables 11-1 and 11-2.4 mm) in thickness. The process is used extensively for soldering copper tubing. 11-2. The torches are used for soldering electrical connections. However. and electrical trades use propane in small cylinders for many heating and soldering applications.(b) The torches for use with air-fuel gas generally are designed to aspirate the proper quantity of air from the atmosphere to provide combustion. Air-fuel gas is used for welding lead up to approximately 1/4 in. refrigeration. For the approximate relation between the tip number and the required oxygen and acetylene pressures. (3) Applications. The greatest field of application in the plumbing and electrical industry. the smaller number always indicates the smaller diameter. The propane flows through the torch at a supply pressure from 3 to 60 psig and serves to aspirate the air.

high velocity flame that is hard to handle and will blow the molten metal from the puddle.8 mm) or more in diameter and 2 in. Too low a gas flow for a given tip size will result in a soft. Too high a gas flow will result in a harsh.
. General. (51 mm) or more in length. ineffective flame sensitive to backfiring. The closer the end of the inner cone is to the surface of the metal being heated or welded. Both adjustments are valuable aids in welding. (2) The inner cone or vivid blue flare of the burning mixture of gases issuing from the tip is called the working flare. (3) The chemical action of the flame on a molten pool of metal can be altered by changing the ratio of the volume of oxygen to acetylene issuing from the tip.NOTE Oxygen pressures are approximately the same as acetylene pressures in the balanced pressure type torch. Most oxyacetylene welding is done with a neutral flame having approximately a 1:1 gas ratio. (1) The oxyfuel gas welding torch mixes the combustible and combustion-supporting gases. b. A range of tip sizes is provided for obtaining the required volume or size of welding flame which may vary from a short. Flare Adjustment. and a reducing action will result from increasing the acetylene flow. (4. the more effective is the heat transfer from flame to metal. Pressures for specific types of mixing heads and tips are specified by the manufacturer. FLAME ADJUSTMENT AND FLAME TYPES a. An oxidizing action can be obtained by increasing the oxygen flow. small diameter needle flame to a flare 3/16 in. 11-3. It provides the means for applying the flame at the desired location. The flame can be made soft or harsh by varying the gas flow.

c. Starting with a neutral flame adjustment. This flame also has a carburizing effect on steel. gas cylinders. the welder can produce the desired acetylene feather by increasing the acetylene flow (or by decreasing the oxygen flow).(1) Torches should be lighted with a friction lighter or a pilot flame. Lighting the Torch. hose. hold it so as to direct the flame away from the operator. Open the acetylene torch valve 1/4-turn and ignite the gas by striking the sparklighter in front of the tip. (3) A practical method of determining the amount of excess acetylene in a reducing flame is to compare the length of the feather with the length of the inner cone. A 2X excess-acetylene flame has an acetylene feather that is twice the length of the inner cone. (2) The neutral flame is obtained most easily by adjustment from an excess-acetylene flame. The feather will diminish as the flow of acetylene is decreased or the flow of oxygen is increased. See figure 11-1. (4) The oxidizing flame adjustment is sometimes given as the amount by which the length of a neutral inner cone should be reduced.
. This flame is actually reducing in nature but is neither carburizing or oxidizing. which is recognized by the feather extension of the inner cone. (1) To start the welding torch. The flame is neutral just at the point of disappearance of the "feather" extension of the inner cone. one tenth. for example. The instructions of the equipment manufacturer should be observed when adjusting operating pressures at the gas regulators and torch valves before the gases issuing from the tip are ignited. or any flammable material. measuring both from the torch tip. Starting with the neutral flare. the welder can increase the oxygen or decrease the acetylene until the length of the inner cone is decreased the desired amount.

Acetylene burning in the inner cone with oxygen supplied by the torch forms carbon monoxide and hydrogen. (1) General.e. The inner cone develops the high temperature required for welding. and water. oxidation of the metal will not occur within this zone. excess acetylene (carburizing). able to combine with and remove oxygen). It is so high (up to 6000°F (3316°C)) that products of complete combustion (carbon dioxide and water) are decomposed into their elements. both carbon monoxide and hydrogen are combustible and will react with oxygen from the air: 2CO + H2 + 1. and excess oxygen (oxidizing).
. The chemical reaction for a one-to-one ratio of acetylene and oxygen plus air is as follows: C2H2 + O2 = 2CO + H2 + Heat This is the primary reaction: however. Continue to open the acetylene valve slowly until the flame burns clean.(2) Since the oxygen torch valve is closed. There is not sufficient oxygen to provide complete combustion. The temperature is the highest just beyond the end of the inner cone and decreases gradually toward the end of the flame. The carbon monoxide burns to form carbon dioxide and hydrogen burns to form water vapor. heat. d. and has a yellowish color. the acetylene is burned by the oxygen in the air. The acetylene flame is long. they burn completely with the oxygen supplied by the surrounding air and form the lower temperature sheath f1ame. They are shown in figure 11-2. which are reducing in character (i. so the flame is smoky and produces a soot of fine unburned carbon. There are three basic flame types: neutral (balanced). (3) Slowly open the oxygen valve.502 = 2CO2 + H2O + Heat This is the secondary reaction which produces carbon dioxide. Types of Flames. The flame changes to a bluish-white and forms a bright inner cone surrounded by an outer flame. Since the inner cone contains only carbon monoxide and hydrogen. As these gases cool from the high temperatures of the inner cone. bushy.. This pure acetylene flame is unsuitable for welding. (4) The temperature of the oxyacetylene flame is not uniform throughout its length and the combustion is also different in different parts of the flame.

(b) The carburizing flame has excess acetylene. This white feather is called the acetylene feather. The neutral flame has a clear.(a) The neutral flame has a one-to-one ratio of acetylene and oxygen. or luminous cone indicating that combustion is complete. It obtains additional oxygen from the air and provides complete combustion. If the
. the inner cone has a feathery edge extending beyond it. well-defined. It is generally preferred for welding.

The carburizing flame may add carbon to the weld metal.2 mm) long at the end of the cone to ensure that the flame is not oxidizing. In some cases. (1. has a shorter envelope and a small pointed white cone. foaming. (b) The neutral or balanced flame is obtained when the mixed torch gas consists of approximately one volume of oxygen and one volume of acetylene. When the flow of acetylene is decreased or the flow of oxygen increased the feather will tend to disappear.acetylene feather is twice as long as the inner cone it is known as a 2X flame. The inner zone consists of a luminous cone that is bluish-white. For most welding operations. The metal flows easily without boiling. while at the end of the outer sheath or envelope the temperature drops to approximately 2300°F (1260°C). which is a way of expressing the amount of excess acetylene. The position of the flame to the molten puddle can be changed. The length of this excess streamer indicates the degree of flame carburization. (a) The welding flame should be adjusted to neutral before either the carburizing or oxidizing flame mixture is set. This neutral flame is obtained by starting with an excess acetylene flame in which there is a "feather" extension of the inner cone. no whitish streamers should be present at the end of the cone. The neutral flame begins when the feather disappears. and the heat controlled in this manner. When welding steel with this flame. the molten metal puddle is quiet and clear. (a) The reducing or carburizing flame is obtained when slightly less than one volume of oxygen is mixed with one volume of acetylene. or sparking. It is obtained by gradually opening the oxygen valve to shorten the acetylene flame until a clearly defined inner cone is visible. This variation within the flame permits some temperature control when making a weld. (3) Reducing or carburizing flame. (c) The oxidizing flame. There are two clearly defined zones in the neutral flame. Surrounding this is a light blue flame envelope or sheath. the temperature at the inner cone tip is approximately 5850°F (3232°C). it is desirable to leave a slight acetylene streamer or "feather" 1/16 to 1/8 in. This flame tends to oxidize the weld metal and is used only for welding specific metals.6 to 3. which has an excess of oxygen. this streamer should be no more than half the length of the inner cone. (2) Neutral flame. The reduction in length of the inner core is a measure of excess oxygen.
. This flame is obtained by first adjusting to neutral and then slowly opening the acetylene valve until an acetylene streamer or "feather" is at the end of the inner cone. (c) In the neutral flame. For a strictly neutral flame. This flame adjustment is used for most welding operations and for preheating during cutting operations.

the metal boils and is not clear. Propylene is intermediate between propane and MAPP gas. MAPP gas has a high heat release in the primary flame. A carburizing flame is advantageous for welding high carbon steel and hard facing such nonferrous alloys as nickel and Monel. an oxidizing flame causes the molten metal to foam and give off sparks. white intermediate cone indicating the amount of excess acetylene. The flow of oxygen is then increased until the inner cone is shortened to about one-tenth of its original length. gives off heat. This type of flare burns with a coarse rushing sound. and brittle. Heating values of fuel gases are shown in table 11-3. the amount of excess oxygen used in this flame must be determined by observing the action of the flame on the molten metal. (4) Oxidizing flame. (c) When a strongly carburizing flame is used for welding. (a) The heat transfer properties of primary and secondary flames differ for different fuel gases. When used in silver solder and soft solder operations. The steel. This indicates that the excess oxygen is combining with the steel and burning it. The temperature of this flame is approximately 6300°F (3482°C) at the inner cone tip. An oxidizing flame should not be used for welding steel because the deposited metal will be porous. (5) MAPP gas flames. (d) A slight feather flame of acetylene is sometimes used for back-hand welding. and a high heat release in the secondary. An oxidizing flame can also be recognized by its distinct hissing sound. oxidized. (a) The oxidizing flame is produced when slightly more than one volume of oxygen is mixed with one volume of acetylene. When cold. the weld has the properties of high carbon steel.(b) The reducing or carburizing flame can always be recognized by the presence of three distinct flame zones. It has a temperature of approximately 5700°F (3149°C) at the inner cone tips. This flame will ruin most metals and should be avoided. except as noted in (c) below. There is a clearly defined bluish-white inner cone. being brittle and subject to cracking. the torch should first be adjusted to a neutral flame. They impart a low temperature soaking heat to the parts being soldered. (b) When applied to steel. and a light blue outer flare envelope. When the flame is properly adjusted. only the intermediate and outer flame cones are used.
. This causes the metal to boil. To obtain this type of flame. the inner cone is pointed and slightly purple. (c) A slightly oxidizing flame is used in torch brazing of steel and cast iron. which is absorbing carbon from the flame. (d) In most cases. A stronger oxidizing flame is used in the welding of brass or bronze.

2:1 or lower. and oxidizing (fig. (c) Adjusting a MAPP gas flame. The inner flame is a very deep blue. Flame adjustment is the most important factor for successful welding or brazing with MAPP gas. the carburizing feather pulls off and disappears.
1. Carburizing flames are obtained with MAPP gas when oxyfuel ratios are around 2.5:1 oxygen-to-fuel ratio. and a louder burning sound. 11-3). As with any other fuel gas. This is the neutral MAPP gas flame for welding. When the feather disappears. 2. As oxygen is increased.3:1. shown in figure 11-3. the oxyfuel ratio is about 2. A carburizing flame looks much the same with MAPP gas or acetylene. there are three basic MAPP gas flames: carburizing. It has a yellow feather on the end of the primary cone. 3. This is an oxidizing MAPP gas
. Slightly carburizing or "reducing" flames are used to weld or braze easily oxidized alloys such as aluminum. Increasing the oxygen flame produces a lighter blue flame. a longer inner cone. or the fuel is turned down. neutral.(b) The coupling distance between the work and the flame is not nearly as critical with MAPP gas as it is with other fuels. The flame remains neutral up to about 2.

b. The slag will have a melting point lower than the metal so it will flow away from the immediate field of action. There is no one flux that is satisfactory for all metals. stainless steel. is a typical oxidizing MAPP gas flame. Welding rods are made for various types of carbon steel. It also maintains cleanliness of the base metal at the welding area and helps remove oxide film on the surface of the metal. They are usually pasty when the metal is quite fluid and at the proper welding temperature. (2) The chemical characteristics and melting points of the oxides of different metals vary greatly. (3) Fluxes are usually in powder form. however. (1) Oxides of all ordinary commercial metals higher melting points than the metals and alloys (except steel) have themselves. These fluxes are often applied by sticking the hot filler metal rod in the flux. The welding area should be cleaned by any method. What will be produced. Sufficient flux will adhere to the rod to provide proper fluxing action as the filler rod is melted in the flame. The flux also serves as a protection for the molten metal against atmospheric oxidation. Good welding rods are designed to permit free flowing metal which will unite readily with the base metal to produce sound. With certain exceptions such as welding or brazing copper and copper alloys. The welding rod. (4) Other types of fluxes are of a paste consistency which are usually painted on the filler rod or on the work to be welded. General. An operator experience with acetylene will immediately adjust the MAPP gas flame to look like the short. The neutral flame is the principle setting for welding or brazing steel. and there is no national standard for gas welding fluxes. plays an important part in the quality of the finished weld. an oxidizing flame is the worst possible flame setting. and other metals for hard surfacing.
. A neutral MAPP gas flame has a primary flame cone abut 1-1/2 to 2 times as long as the primary acetylene flame cone. OXYFUEL WELDING FLUXES a. An efficient flux will combine with oxides to form a fusible slag. bronze. They are categorized according to the basic ingredient in the flux or base metal for which they are to be used. aluminum. intense blue flame typical of the neutral acetylene flame setting. whatever the fuel gas used. 11-5.flare. 11-4. clean welds of the correct composition. which is melted into the welded joint. It combines with base metal oxides and removes them. OXYFUEL WELDING RODS a.

Fluxes differ in their composition according to the metals with which they are to be used. Fluxes are available from welding supply companies and should be used in accordance with the directions accompanying them. the heat can be carefully balanced to melt the end of the rod and the side walls of the plate into a uniformly distributed molten puddle. The flame is pointed in the direction of welding and directed between the rod and the molten puddle. The metal is distributed evenly to both edges being welded by the motion of the tip. Equal parts of a carbonate of soda and bicarbonate of soda make a good compound for this purpose. For sheet aluminum welding. The ideal flux has exactly the right fluidity when the welding temperature has been reached. In this method. A good flux is required with aluminum. This position permits uniform preheating of the plate edges immediately ahead of the molten puddle. The melting point of a flux must be lower than that of either the metal or the oxides formed. Such a flux will remain close to the weld area instead of flowing all over the base metal for some distance from the weld. By moving the torch and the rod in opposite semicircular paths. Nonferrous metals usually require a flux. a slag forms on the surface of the puddle. In cast iron welding. Borax which has been melted and powdered is often used as a flux with copper alloys. all traces of the flux should be removed. The torch is held at approximately a 45 degree angle from the vertical in the direction of welding. The heat which is reflected backwards from the rod keeps the metal molten. b. c. After welding aluminum. FOREHAND WELDING a. so that it will be liquid. it is customary to dissolve the flux in water and apply it to the rod. The flux will protect the molten metal from atmospheric oxidation. The flux serves to break this up.(5) Welding rods with a covering of flux are also available.
. The rod is dipped into the leading edge of the puddle so that enough filler metal is melted to produce an even weld joint. Copper also requires a filler rod containing enough phosphorous to produce a metal free from oxides. as shown in figure 11-4. the welding rod precedes the torch. 11-6. because there is a tendency for the heavy slag formed to mix with the melted aluminum and weaken the weld.

some difficulties in welding heavier plates using the forehand method are: (1) The edges of the plate must be beveled to provide a wide V with a 90 degree included angle. The welding rod is between the flame and the molten puddle. because it provides better control of the small weld puddle. (9. In contrast. and fusion of the weld metal to the base metal. A great deal of pipe welding is done using the forehand technique. the forehand method is recommended for welding material up to 1/8 in. good penetration. 11-7. This position requires less transverse motion than is used in forehand welding. with the flame directed at the molten puddle. The torch is held at approximately a 45 degree angle from the vertical away from the direction of welding. The puddle of molten metal is small and easily controlled. (2) Because of this wide V. (3.2 mm) thick. the torch precedes the welding rod. a relatively large molten puddle is required. as shown in figure 11-5. It is difficult to obtain a good joint when the puddle is too large. BACKHAND WELDING a. In this method.b. resulting in a smoother weld at both top and bottom. This edge preparation is necessary to ensure satisfactory melting of the plate edges.
.5 mm) wall thick-nesses. In general. even in 3/8 in.

In some cases. the fillet has wide usage. (1) The fillet weld is the most popular of all types of welds because there is normally no preparation required. 11-8.2 mm) and thicker is welded. This technique increases speed of making pipe joints where the wall thickness is 1/4 to 5/16 in. the double fillet can actually produce a full-penetration weld joint. On corner joints. Increased speeds and better control of the puddle are possible with backhand technique when metal 1/8 in. the fillet weld is the least expensive. (3. (6. and the corner joint without preparation. Backhand welding is sometimes used in surfacing operations. The use of the fillet for making all five of the basic joints is shown by figure 11-6. the tee joint. even though it might require more filler metal than a groove weld since the preparation cost would be less.9 mm) and groove angle is less than normal. particularly for corner and tee joints. Fillet welds are also used in conjunction with groove welds. It can be used for the lap joint. based on the study of speeds normally achieved with this technique and on greater ease of obtaining fusion at the weld root. Since these are extremely popular. Backhand welding may be used with a slightly reducing flame (slight acetylene feather) when desirable to melt a minimum amount of steel in making a joint. The increased carbon content obtained from this flame lowers the melting point of a thin layer of steel and increases welding speed.
.4 to 7. General. FILLET WELDING a.b.

yet equal strength will result. For example. However. (9. which relates to the throat dimension. the throat length must be calculated and is the shortest distance between the root of the fillet and the theoretical face of the fillet.(2) The fillet weld is expected to have equal length legs and thus the face of the fillet is on a 45 degree angle. The root penetration is also ignored unless a deep penetrating process is used. the strength of the fillet is based on the shortest or throat dimension which is 0.8 mm) fillet. If semi-or fully-automatic application is used. in which case it is specified by the two leg lengths. This is not always so. Such reductions can be utilized only when strict welding procedures are enforced. On the 45 degree or normal type of fillet. since a fillet may be designed to have a longer base than height. For fillets having unequal legs. the size of the fillet can be reduced.
(3) Under these circumstances. doubling the fillet size will increase its cross-sectional area and weight four times. (4. See figure 11-7 for details about the weld. or weight. the extra penetration can be considered. (9. This illustrated in figure 11-8. the reinforcement is ignored. however. The strength of the fillet weld is determined by its failure area. since it doubles the throat dimension and area. In calculating the strength of fillet welds. Doubling the size or leg length of a fillet will double its strength. which shows the relationship to throat-versus-cross-sectional area. of a fillet weld.707 x the leg length.5 mm) fillet is twice as strong as a 3/16 in. the 3/8 in.5 mm) fillet requires four times as much weld metal. a 3/8 in.
.

b. rather than because of strength requirements. Intermittent fillets are sometimes used when the size is minimum. This applies to tee joints.
. (5) Single fillet welds are extremely vulnerable to cracking if the root of the weld is subjected to tension loading. corner joints. This is shown by figure 11-6.8 mm) pitch (center to center of intermittent welds) could be reduced to a continuous 3/16 in.8 mm) fillet. (9. and the strength would be the same. but the amount of weld metal would be only half as much. In some situations. For example.5 mm) fillet 6 in. the minimum size of the fillet must be based on practical reasons rather than the theoretical need of the design. and lap joints. or for practical reasons. by pointing the flame more at the bottom plate than at the edge of the upper plate. A different welding technique is required for fillet welding than for butt joints because of the position of the parts to be welded. there is a tendency for the top plate to melt before the bottom plate because of heat rising. This can be avoided. which prohibit the tensile load from being applied to the root of the fillet.4 mm) long on a 12 in. (304. Large intermittent fillets are not recommended because of the volume-throat dimension relationship mentioned previously. the fillet size is sometimes governed by the thickness of the metals joined. based on code. a 3/8 in. (4. Many intermittent welds are based on a pitch and length so that the weld metal is reduced in half. When welding is done in the horizontal position. Notice the F (force) arrowhead. The simple remedy for such joints is to make double fillets. Both plates must reach the welding temperature at the same time. (152. however.(4) In design work.

. The American Welding Society has defined the four basic welding positions as shown in figure 11-9.c. It is important that the flame not be pointed directly at the inner corner of the fillet. The flame should be pointed ahead slightly in the direction in which the weld is being made and directed at the lower plate. Proper description and definition is necessary since welding procedures must indicate the welding position to be performed. It must be done in the position in which the part will be used. 11-9. and welding process selection is necessary since some have all-position capabilities whereas others may be used in only one or two positions. It is essential in this form of welding that fusion be obtained at the inside corner or root of the joint. the flame should be concentrated on the lower plate until the metal is quite red. This will cause excessive amount of heat to build up and make the puddle difficult to control. Then the flame should be directed so as to bring both plates to the welding temperature at the same time. in the corner. d. or on the floor. In making the weld. Often that may be on the ceiling. Welding cannot always be done in the most desirable position. To start welding. a modified form of backhand technique should be used. The welding rod should be kept in the puddle between the completed portion of the weld and the flame. HORIZONTAL POSITION WELDING a.

A joint in horizontal position will require considerably more practice than the previous techniques. For a fillet weld. Align the plates and tack weld at both ends (fig. but the weld type dictates the complete definition.
. The combination of these opposing factors makes it difficult to apply a uniform deposit to this joint.b. The heat from the torch rises to the upper side of the joint. 11-10). c. In horizontal welding. and permits faster solidification of the weld metal. however. welding is performed on the upper side of an approximately horizontal surface and against an approximately vertical surface. Butt welding in the horizontal position is a little more difficult to master than flat position. This is due to the tendency of molten metal to flow to the lower side of the joint. the face of the weld lies in an approximately vertical plane. For a groove weld. This prevents excessive flow of the metal to the lower side of the joint. It is. thereby holding the molten metal in a plastic state. d. important that the technique be mastered before passing on to other types of weld positions. The torch should move with a slight oscillation up and down to distribute the heat equally to both sides of the joint. the weld axis is approximately horizontal.

This type of welding is performed from the upper side of the joint.
. FLAT POSITION WELDING a. the flare motion. Bead Welds. and position of the welding flame above the molten puddle should be carefully maintained. b. (2) Narrow bead welds are made by raising and lowering the welding flare with a slight circular motion while progressing forward. The face of the weld is approximately horizontal. General. (1) In order to make satisfactory bead welds on a plate surface. The welding torch should be adjusted to give the proper type of flame for the particular metal being welded. tip angle. 11-11 and 11-12).11-10. The tip should form an angle of approximately 45 degrees with the plate surface. The flame will be pointed in the welding direction (figs.

The size of the puddle should not be too large because this will cause the flame to burn through the plate. A properly made bead weld. either increase the angle between the tip and the plate surface. will be slightly below the upper surface of the plate.(3) To increase the depth of fusion. A bead weld with filler rod shows a buildup on the surface. without filler rod. or decrease the welding speed.
.

The torch should be moved slightly from side to side to obtain good fusion. 1/8 to 1/4 1/4 to 5/8 5/8 to 7/8 7/8 to 1-1/8 Number of passes 1 2 3 4
(4) The position of the welding rod and torch tip in making a flat position butt joint is shown in figure 11-13. Butt Welds. in.
(5) Care should be taken not to overheat the molten puddle. 11-8) in butt welding steel plates: Plate thickness. a molten puddle of a given size can be carried along the joint. (3) The following guide should be used for selecting the number of passes (fig. This will ensure both complete penetration and sufficient filler metal to provide some reinforcement at the weld. The motion of the flame should be controlled so as to melt the side walls of the plates and enough of the welding rod to produce a puddle of the desired size. The welding rod is inserted into the puddle and the base plate and rod are melted together.(4) A small puddle should be formed on the surface when making a bead weld with a welding rod (fig.
. 11-12). c. This